Refrigeration system utilizing incomplete evaporation of refrigerant in evaporator

ABSTRACT

A refrigeration system allows the refrigerant to circulate through a closed circulation channel. A dry evaporator is incorporated in the circulation channel. The dry evaporator is designed to keep a quality smaller than 1.0 in evaporating the refrigerant. The quantity of heat transfer per unit area, namely, a heat transfer coefficient depends on the quality. The heat transfer coefficient remarkably drops when the quality of the refrigerant exceeds a predetermined threshold level before the quality actually reaches 1.0. The quality of the refrigerant kept below the predetermined threshold level during vaporization of the refrigerant in the dry evaporator allows a reliable establishment of a higher performance of cooling. On the other hand, if a refrigerant completely evaporates in a dry evaporator in a conventional manner, the heat transfer coefficient of the refrigerant remarkably drops after the quality of the refrigerant exceeds the predetermined threshold level. Accordingly, the conventional dry evaporator is forced to absorb heat at a lower heat transfer coefficient, as compared with the present dry evaporator.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a refrigeration system of aclosed cycle, including: a circulation channel through which arefrigerant circulates; and a dry evaporator incorporated in thecirculation channel so as to contact a target heating object.

[0003] 2. Description of the Prior Art

[0004] A refrigeration system of a closed cycle is well known to includea so-called dry evaporator. The refrigeration system is often employedin an interior air conditioner, for example. The evaporation of arefrigerant can be promoted within the dry evaporator under a lowpressure, so that atmosphere around the dry evaporator can be cooleddown. The refrigerant completely evaporates within the dry evaporator insuch an interior air conditioner. The quality of the refrigerant isforced to reach 1.0 within the dry evaporator. Only the refrigerant ofgas state is intended to be discharged from the dry evaporator.

[0005] A cooling system is in general incorporated in a large-sizedcomputer such as a supercomputer and a main frame. The cooling system isdesigned to cool a semiconductor device module such as a multichipmodule (MCM). Acceleration of operating clocks and a higher density ofelectronic elements are predicted to induce the increased quantity ofheat in the semiconductor device module. A higher performance of coolingis expected in the cooling system. It is believed that it becomesdifficult for a conventional refrigeration system to reliably restrainan increase in the temperature of the semiconductor device module.

[0006] The performance of cooling in the dry evaporator may beconsidered based on the quantity of heat transfer per unit area, namely,a heat transfer coefficient. A higher heat transfer coefficient servesto reliably prevent the semiconductor device module from an excessiveincrease in the temperature, even when the semiconductor device modulesuffers from an extreme generation of heat. Heretofore, no specificproposal has been made to increase the quantity of heat transfer perunit area in the technical field of a refrigeration system of a closedcycle.

SUMMARY OF THE INVENTION

[0007] It is accordingly an object of the present invention to provide arefrigeration system capable of achieving a higher performance ofcooling as compared with a prior art refrigeration system.

[0008] According to a first aspect of the present invention, there isprovided a refrigeration system comprising: a circulation channelthrough which a refrigerant circulates; and a dry evaporatorincorporated in the circulation channel and designed to keep a qualitysmaller than 1.0 in evaporating the refrigerant.

[0009] In general, the quantity of heat transfer per unit area, namely,a heat transfer coefficient depends on the quality. The heat transfercoefficient remarkably drops when the quality of the refrigerant exceedsa predetermined threshold level before the quality actually reaches 1.0.If the quality of the refrigerant is kept below the predeterminedthreshold level during vaporization of the refrigerant in the dryevaporator, the dry evaporator is allowed to reliably establish a higherperformance of cooling. On the other hand, if a refrigerant completelyevaporates in a dry evaporator in a conventional manner, the heattransfer coefficient of the refrigerant remarkably drops after thequality of the refrigerant exceeds the predetermined threshold level.Accordingly, the conventional dry evaporator is forced to absorb heat ata lower heat transfer coefficient, as compared with the dry evaporatorof the first aspect. It should be noted that the threshold quality of arefrigerant employed can be set, at a level below 1.0, in an appropriatemanner based on the kind of a refrigerant and the capability of coolingrequired in the dry evaporator.

[0010] According to a second aspect of the present invention, there isprovided a refrigeration system comprising: a circulation channelthrough which a refrigerant circulates; a dry evaporator incorporated inthe circulation channel and contacting a target heating object; and asubsidiary evaporator incorporated in the circulation channel downstreamof the dry evaporator.

[0011] It is not necessary to completely evaporate the refrigerant inthe dry evaporator of this type of the refrigeration system. Thesubsidiary evaporator may be employed to accomplish the completevaporization of the refrigerant, so that the quality of 1.0 isestablished in the refrigerant discharged out of the subsidiaryevaporator. If such a dry refrigerant is supplied to a compressordownstream of the subsidiary evaporator, the compressor can reliably beprevented from a compression of a liquid, which is harmful to thecompressor. The dry evaporator contacting a target heating object isallowed to discharge the refrigerant of gas-liquid mixture state.Specifically, the quality of the refrigerant can be kept below apredetermined threshold level during vaporization of the refrigerant inthe dry evaporator in the aforementioned manner, so that the dryevaporator is allowed to reliably establish a higher performance ofcooling.

[0012] According to a third aspect of the present invention, there isprovided a method of refrigeration comprising vaporizing a refrigerantwithin a dry evaporator incorporated in a circulation channel, throughwhich the refrigerant circulates, so as to allow the refrigerant ofgas-liquid mixture state to flow out of the dry evaporator.

[0013] The method of refrigeration allows the dry evaporator todischarge the refrigerant after incomplete vaporization of therefrigerant in the dry evaporator. The quality of the refrigerant can bekept below a predetermined threshold level during vaporization of therefrigerant in the dry evaporator in the aforementioned manner, so thatthe dry evaporator is allowed to reliably establish a higher performanceof cooling.

[0014] The method of refrigeration may further comprise heating therefrigerant flowing out of the dry evaporator so as to completelyevaporate the refrigerant of liquid state. If the refrigerant cancompletely be evaporated before it is introduced into a compressorincorporated in the circulation channel downstream of the dryevaporator, the compressor can reliably be prevented from a compressionof a liquid. The compression of a liquid is harmful to the compressor,as conventionally known.

[0015] According to a fourth aspect of the present invention, there isprovided a refrigeration system comprising: a circulation channelthrough which a refrigerant circulates; a dry evaporator incorporated inthe circulation channel so as to contact a target heating object; arefrigerant outlet defined in the dry evaporator and designed todischarge the refrigerant of gas-liquid mixture state; and a gas-liquidseparation filter incorporated in the refrigerant outlet.

[0016] Even when the refrigerant is incompletely evaporated in the dryevaporator in this refrigeration system, the gas-liquid separationfilter serves to reliably establish the quality of 1.0 for therefrigerant discharged from the dry evaporator. If such a dryrefrigerant is introduced into a compressor incorporated in thecirculation channel downstream of the dry evaporator, the compressor canreliably be prevented from a compression of a liquid, which is harmfulto the compressor. The dry evaporator contacting a target heating objectis allowed to discharge the refrigerant of gas-liquid mixture state.Specifically, the quality of the refrigerant can be kept below apredetermined threshold level during vaporization of the refrigerant inthe dry evaporator in the aforementioned manner, so that the dryevaporator is allowed to reliably establish a higher performance ofcooling.

[0017] The respective aforementioned refrigeration systems may include adry evaporator, comprising: a casing defining a closed space; arefrigerant inlet defined in the casing so as to open at a wall surface;a refrigerant outlet defined in the casing so as to open at a wallsurface; and a group of fins inwardly protruding from an inner surfaceof the casing so as to define a plurality of refrigerant passagesextending in parallel from the refrigerant inlet toward the refrigerantoutlet, for example. The group of fins serves to enlarge a heat transferarea or contact area between the casing and the refrigerant in the dryevaporator of this type. Heat can reliably be transferred from thecasing to the refrigerant in an efficient manner.

[0018] In this case, the refrigerant passage preferably gets shorter ata position remoter from a straight line extending from the refrigerantinlet to the refrigerant outlet. In general, the refrigerant dischargedout of the refrigerant inlet is supposed to flow along the straight linetoward the refrigerant outlet, because the maximum pressure can bemaintained along the shortest path. The remoter from the straight linethe refrigerant passage is located at, the less pressurized force can beapplied to the refrigerant passing through the refrigerant passage, asconventionally known. If the refrigerant passage gets shorter, therefrigerant passage may be released from a larger loss of the appliedpressure. The shorter refrigerant passage at a position remoter from thestraight line in the aforementioned manner is supposed to equallydistribute the refrigerant to the respective refrigerant passage definedbetween the adjacent fins. The vaporization of the refrigerant canuniformly be achieved within the closed space.

[0019] In place of the aforementioned shorter refrigerant passage at alocation remoter from the straight line, a refrigerant passage may getwider at a position remoter from the straight line. The widerrefrigerant passage is supposed to reduce a larger loss of the appliedpressure, so that the refrigerant is equally distributed to therespective refrigerant passage defined between the adjacent fins in theaforementioned manner. The vaporization of the refrigerant can uniformlybe achieved within the closed space.

[0020] Alternatively, a dry evaporator may include: a casing defining aclosed space between a top plate and a bottom plate and contacting atarget heating object at the bottom plate; an intermediate platedisposed between the top and bottom plates within the closed space; avaporization chamber defined between the intermediate and bottom plates;a refrigerant inlet defined in the top plate; an introduction chamberdefined between the top and intermediate plates and extending from therefrigerant inlet toward the vaporization chamber; and a dischargechamber defined between the top and intermediate plates and extendingfrom the vaporization chamber toward the refrigerant outlet.

[0021] In general, the refrigerant flowing out of the refrigerant outletcan be maintained at a temperature lower than that of the refrigerantflowing through the refrigerant inlet in the dry evaporator, since thenegative pressure can be applied to the refrigerant outlet because ofthe operation of a compressor. The intermediate plate serves toestablish a heat exchange between the refrigerants in the refrigerantinlet and outlet based on the difference in temperature. It is possibleto restrain variation in the quality of the refrigerant headed towardthe vaporization chamber from the refrigerant inlet. A still higherperformance of cooling can be achieved in the dry evaporator.

[0022] In the above-described dry evaporator, a space between the topand intermediate plates may be set smaller than a space between thebottom and intermediate plates. The smaller space between the top andintermediate plates is expected to accelerate the loss of pressure forthe refrigerant in the refrigerant introduction chamber, so that therefrigerant of the liquid state can be prevented from vaporization tothe utmost before it is introduced into the vaporization chamber. Astill higher performance of cooling can be achieved in the dryevaporator.

[0023] In the case where the space is reduced between the top andintermediate plates, it is preferable that the dry evaporator furthercomprises: an introduction opening defined by an edge of theintermediate plate and designed to connect the introduction andvaporization chambers to each other; and a dike extending along the edgeof the intermediate plate so as to swell from the intermediate plate atits surface receiving a refrigerant within the introduction chamber. Thedike serves to reliably accelerate the loss of pressure for therefrigerant in the introduction chamber. Moreover, the dike is alsoexpected to establish a uniform flow of the refrigerant over the edge ofthe intermediate plate, namely, a uniform inflow of the refrigerant intothe introduction opening.

[0024] The introduction chamber may be designed to by degree expand asit gets closer to the vaporization chamber. The introduction chamber ofthis type is expected to reliably establish a uniform inflow of therefrigerant into the vaporization chamber. The refrigerant uniformlyspreads over the entire vaporization chamber. Additionally, thedischarge chamber may be designed to by degree narrow as it gets closerto the refrigerant outlet. The discharge chamber of this type isexpected to contribute to establishment of a uniform inflow of therefrigerant into the vaporization chamber.

[0025] A plurality of refrigerant passages may be defined within theintroduction chamber so as to respectively extend from the refrigerantinlet toward the vaporization chamber. The refrigerant passages serve touniformly distribute the refrigerant before it is introduced into thevaporization chamber.

[0026] An expanded passage is preferably connected to a downstream endof the refrigerant passage. The expanded passage serves to remarkablyaccelerate the loss of pressure for the refrigerant, so that thevaporization of the refrigerant flowing into the vaporization chambercan be promoted. A performance of cooling can still be improved in thedry evaporator.

[0027] Furthermore, the dry evaporator may comprise: a casing defining aclosed space between a top plate and a bottom plate and contacting atarget heating object at the bottom plate; an intermediate platedisposed between the top and bottom plates within the closed space andconnected to an inner surface of the casing; a vaporization chamberdefined between the intermediate and bottom plates; a discharge chamberdefined between the top and intermediate plates; an inlet duct defininga refrigerant introduction passage penetrating through the dischargechamber so as to reach the vaporization chamber; and an outlet ductsurrounding the inlet duct so as to define a refrigerant dischargepassage extending from the discharge chamber. The dry evaporator servesto establish a heat exchange between the refrigerant flowing through therefrigerant introduction passage and the refrigerant flowing through therefrigerant discharge passage based on the heat transfer through thewall of the inlet duct. It is thus possible to restrain variation in thequality of the refrigerant headed toward the vaporization chamber fromthe refrigerant introduction passage to the utmost.

[0028] Alternatively, the refrigeration system may for example comprise:a circulation channel through which a refrigerant circulates; a dryevaporator incorporated in the circulation channel and contacting atarget heating object at its bottom plate; a vaporization chamberdefined within the dry evaporator for inducing a flow of the refrigerantalong the bottom plate in a horizontal direction; and a flow controllerincorporated in the circulation channel for discharging the refrigerantat a flow enough to establish a gas-liquid separation within thevaporization chamber. When the flow rate or current of the refrigerantintroduced into the vaporization chamber is adjusted in this manner, therefrigerant of liquid state, namely, the refrigerant liquid is allowedto flow along the upper surface of the bottom plate within thevaporization chamber under the influence of the gravity. Accordingly,the refrigerant liquid is allowed to uniformly spread over the entireupper surface of the heat transfer or bottom plate. A higher performanceof cooling can thus be achieved uniformly over the broader area of thebottom plate.

[0029] Furthermore, when the gas-liquid separation is intended withinthe vaporization chamber, the dry evaporator may comprise: a casingcontacting a target heating object at a vertical heat transfer plate; avaporization chamber defined adjacent the heat transfer plate within thecasing; a refrigerant inlet opened at an inner surface of thevaporization chamber; a refrigerant outlet opened at the inner surfaceof the vaporization chamber at a location above the refrigerant inlet;and a plurality of fins integrally formed on the heat transfer platewithin the vaporization chamber so as to define a plurality ofrefrigerant passages respectively extending in a vertical direction fromthe refrigerant inlet toward the refrigerant outlet.

[0030] A refrigerant discharged from the refrigerant inlet is allowed toflow upward within the vaporization chamber along the heat transferplate and to finally reach the refrigerant outlet. If the gas-liquidseparation is realized in the vaporization chamber, the refrigerantliquid falls on the bottom of the vaporization chamber under theinfluence of the gravity. The refrigerant liquid received on the bottomplate can uniformly be distributed into the respective refrigerantpassages defined between the adjacent fins in the dry evaporator. Whenthe dry evaporator of this type is employed in the refrigeration systemof a closed cycle, a flow controller may be incorporated in thecirculation channel for discharging the refrigerant at a flow enough toestablish the gas-liquid separation within the vaporization chamber.

[0031] The dry evaporator of this type may further comprise: a bypassopening formed in the casing so as to open at a lowest position in thevaporization chamber; a duct connected to the casing so as to define adischarge channel extending from the refrigerant outlet; and a bypasschannel connecting the bypass opening and the discharge channel to eachother. For example, a lubricating agent such as oil may involuntarily beintroduced into the vaporization chamber in the dry evaporator employedin the refrigeration system. The oil stored in the vaporization chambercan be led to the discharge channel or the circulation channel throughthe bypass channel under the influence of the difference in pressurebetween the refrigerant inlet and outlet. It is possible to prevent theoil, discharged from the compressor, from staying within thevaporization chamber.

[0032] Furthermore, when the gas-liquid separation is intended in thevaporization chamber, a dry evaporator still may comprise: a casingdefining a vaporization chamber between a vertical heat transfer plateand a vertical back plate and contacting a target heating object at theheat transfer plate; a partition plate disposed between the heattransfer plate and the back plate so as to divide an upper portion ofthe vaporization chamber into an introduction space adjacent the heattransfer plate and a discharge space adjacent the back plate; arefrigerant inlet opened at the inner surface of the introduction space;and a refrigerant outlet opened at the inner surface of the dischargespace. In this case, the depth of the lower portion of the vaporizationchamber is set larger than the space or distance measured between theheat transfer plate and the partition plate. Here, the depth should bemeasured from the lower edge of the partition plate in the verticaldirection. The dry evaporator of this type enables a jagged increase inthe sectional area of the vaporization chamber when the refrigerantflows around the lower edge of the partition plate. The remarkableenlargement of the sectional area promotes the gas-liquid separation ofthe refrigerant in the vaporization chamber. Here, the sectional area ofthe vaporization chamber is measured based on a profile in a planeperpendicular to the direction of the flow or current of therefrigerant. When the dry evaporator of this type is employed in therefrigeration system of a closed cycle, a flow controller may beincorporated in the circulation channel for discharging the refrigerantat a flow enough to establish the gas-liquid separation within thevaporization chamber.

[0033] Otherwise, the dry evaporator may comprise a casing contacting atarget heating object at a vertical heat transfer plate; and a microchannel formed on the heat transfer plate within the casing so as toextend in a vertical direction, said micro channel having a width enoughto realize a capillary action of a refrigerant.

[0034] The dry evaporator of this kind allows the refrigerant liquid toascend along the micro channel with the assistance of the capillaryaction overcoming the gravity. Accordingly, the heat transfer plate isallowed to hold the refrigerant liquid over a broader area irrespectiveof the level of the refrigerant liquid at the bottom of the casing. Therefrigerant liquid is forced to vaporize in an efficient manner by heattransmitted to the heat transfer plate. The vaporization of therefrigerant liquid can thus be accelerated. When the dry evaporator ofthis type is employed in a refrigeration system of a closed cycle, aflow controller may be incorporated in the circulation channel fordischarging the refrigerant at a flow enough to establish the gas-liquidseparation within the vaporization chamber.

[0035] Furthermore, a dry evaporator may include: a casing contacting atarget heating object at a heat transfer plate; a first wall surfacedefined on the heat transfer plate within the casing so as to extendfrom a datum line; and a second wall surface connected to the first wallsurface at the datum line and opposed to the first wall surface. Thespace between the first and second wall surfaces gets larger as thesecond wall surface is distanced apart from the datum line. A microchannel is defined between the first and second wall surfaces so as toestablish a capillary action of a refrigerant.

[0036] The dry evaporator enables generation of a larger surface tensionat the surface of the refrigerant liquid facing the datum line when therefrigerant liquid is introduced between the first and second wallsurfaces. The refrigerant liquid is sucked toward the datum line betweenthe first and second wall surfaces with the assistance of the surfacetension. A larger quantity of the refrigerant liquid can thus be heldbetween the first and second wall surfaces. The vaporization of therefrigerant liquid can be accelerated.

[0037] An expanded groove may be defined at least on any of the firstand second wall surfaces so as to extend along the datum line within themicro channel. The expanded groove serves to reliably hold a stilllarger quantity of the refrigerant liquid introduced between the firstand second wall surfaces. The vaporization of the refrigerant liquid canstill further be accelerated.

[0038] A dry evaporator may include: a casing contacting a targetheating object at a heat transfer plate; a first erosion surface definedon the heat transfer plate within the casing; and a second erosionsurface opposed to the first erosion surface so as to define a microchannel between the first and second erosion surfaces. A fine asperitycan be established on the first and second erosion surfaces. Such a fineasperity serves to achieve an enlarged heat transfer area over the heattransfer plate and an improved wetness to the refrigerant liquid. Thevaporization of the refrigerant liquid can still further be accelerated.

[0039] Alternatively, a dry evaporator may include: a casing contactinga target heating object at a heat transfer plate; a first wall surfacedefined on the heat transfer plate within the casing; a second wallsurface opposed to the first wall surface so as to define a microchannel between the first and second wall surfaces; and heat conductivefine particles adhered to the first and second wall surfaces,respectively. The heat conductive fine particles serve to achieve anenlarged heat transfer area over the heat transfer plate and an improvedwetness to the refrigerant liquid. The vaporization of the refrigerantliquid can thus be accelerated.

[0040] Furthermore, a refrigeration system may comprise: a circulationchannel through which a refrigerant circulates; a compressorincorporated in the circulation channel and designed to discharge therefrigerant of gas state at a high pressure; a dry evaporatorincorporated in the circulation channel so as to contact a targetheating object at a heat transfer plate; a jet nozzle inserting a tipend into an interior of the dry evaporator; and a bypass channeldiverging from the circulation channel downstream of the compressor soas to supply the refrigerant of gas state toward the jet nozzle.

[0041] During the operation of the compressor, the refrigerant of gasstate, namely, the refrigerant gas, discharged from the compressor at ahigh pressure, is supplied to the jet nozzle through the bypass channel.The supplied refrigerant gas can be discharged out of the jet nozzletoward the refrigerant of liquid state at the bottom of the dryevaporator, for example. Drops of the refrigerant liquid may splashupward from the surface of the refrigerant liquid at the bottom of thedry evaporator. If the splashed refrigerant liquid is allowed to stickto the heat transfer plate, the refrigerant liquid can be held on theheat transfer plate over a broader area. The vaporization of therefrigerant liquid can be promoted in the dry evaporator.Simultaneously, the discharged refrigerant gas may also lead to stir ofthe refrigerant liquid at the bottom of the dry evaporator. The stir ofthe refrigerant liquid may contribute to a uniform distribution of therefrigerant liquid within the dry evaporator.

[0042] A flow controller, such as an electronic controlled valve, may beincorporated in the bypass channel. If the flow controller is allowed tocontrol the flow or current of the refrigerant gas passing through thebypass channel, the jet amount of the refrigerant gas introduced intothe dry evaporator at a high pressure can properly be adjusted. Thevapor pressure within the dry evaporator. If the vapor pressure canproperly be controlled in this manner, the boiling point of therefrigerant can properly be adjusted in the dry evaporator.

[0043] The aforementioned refrigeration system may be employed to cool asemiconductor device module such as a multichip module (MCM) in alarge-sized computer such as a supercomputer, a main frame, and thelike. In employment of the refrigeration system, a semiconductor devicemodule may be prepared to include: a printed circuit board; asemiconductor element mounted on the printed circuit board; a dryevaporator contacting the semiconductor element and applicable to arefrigeration system of a closed cycle; and a heat insulator membercontaining the dry evaporator so as to fix the dry evaporator to theprinted circuit board.

[0044] If the dry evaporator can be fixed to the printed circuit boardin this manner, the semiconductor device module and the dry evaporatorcan be handled as a unit. The operability can be improved in replacementor maintenance of the semiconductor device module. The heat insulatormember serves to prevent condensation and/or frost over the surface ofthe dry evaporator.

[0045] The heat insulator member may be divided into a first half piececontaining the printed circuit board, and a second half piece containingthe dry evaporator and detachably coupled to the first half piece.Detachment of the second half piece from the first half piece enablesexposure of the surface of the printed circuit board. The semiconductorelement or chip can be maintained or replaced on the printed circuitboard without disturbance from the heat insulator member. Theoperability in replacement and/or maintenance of the semiconductordevice module can further be improved.

[0046] A heater may be incorporated in the heat insulator member in theaforementioned semiconductor device module. The heater is designed toheat the heat insulator member. Incorporation of the heater in thismanner thus enables reduction in the thickness or volume of the heatinsulator member, when the prevention of condensation and/or frost isintended on the surface of the dry evaporator. The semiconductor devicemodule can be made compact. The compact semiconductor device module maycontribute to a higher density in arrangement of the semiconductordevice module.

[0047] A heat conductive member may be interposed between the heater andthe dry evaporator. The heat conductive member is preferably designed tohave a property allowing heat to conduct at a first specific thermalconductivity in a vertical direction oriented from the heater to the dryevaporator and to conduct at a second specific thermal conductivitylarger than the first specific thermal conductivity in a planeperpendicular to the vertical direction. When heat from the heater istransferred to the heat conductive member of the type, the heatconductive member serves to spread the heat from the heater over abroader area along the plane perpendicular to the vertical directionwithin the heat insulator member. Irrespective of the size of theheater, the heat insulator member can be heated over the broader area.On the other hand, the heat from the heater hardly reaches the dryevaporator, so that the performance of cooling in the dry evaporator isprevented from unnecessarily being consumed.

[0048] In addition, a semiconductor device module may comprise: aprinted circuit board; a semiconductor element mounted on the upper sideof the printed circuit board; a dry evaporator contacting thesemiconductor element and applicable to a refrigeration system of aclosed cycle; an input/output pin standing on the lower side of theprinted circuit board; and a heater attached to the lower side of theprinted circuit board.

[0049] In general, the input/output pin is made from a metallicmaterial. The metallic input/output pin is easily cooled down under theinfluence of performance of cooling by the dry evaporator. If theinput/output pin is excessively cooled down, the surface of theinput/output pin tends to suffer from condensation and/or frost.Attachment of the heater to the lower side of the printed circuit boardenables transmission of heat to the input/output pin, so that theinput/output pin can be prevented from generation of condensation and/orfrost on its surface.

[0050] Furthermore, a semiconductor device module may comprise: aprinted circuit board; a semiconductor element mounted on the upper sideof the printed circuit board; a dry evaporator contacting thesemiconductor element and applicable to a refrigeration system of aclosed cycle; an input/output pin standing on the lower side of theprinted circuit board; and a heat insulator member containing theinput/output pin. The heat insulator member contributes to prevention ofcondensation and/or frost on the surface of the input/output pin.

[0051] Furthermore, a semiconductor device module may comprise: aprinted circuit board; a semiconductor element mounted on the printedcircuit board; a heat transfer plate contacting the semiconductorelement; a dry evaporator contacting the heat transfer plate andapplicable to a refrigeration system of a closed cycle; a bolt forfixation received in a through bore defined in the heat transfer plate;and a low heat conductive member interposed between the heat transferplate and the bolt. With this arrangement, when the dry evaporator isattached to the printed circuit board, it is possible to restrain a heattransfer between the dry evaporator and the printed circuit board.Accordingly, the printed circuit board can be prevented from anexcessive cooling under the influence of the dry evaporator.

[0052] Furthermore, a semiconductor device module may comprise: aprinted circuit board; a semiconductor element mounted on the printedcircuit board; a dry evaporator contacting the semiconductor element andapplicable to a refrigeration system of a closed cycle; and a heatercontacting the dry evaporator.

[0053] In general, when the semiconductor device module is to bereplaced or maintained, the semiconductor device module should return tothe room temperature. If the semiconductor device module is exposed tothe normal atmosphere before it has returned to the room temperature,condensation and/or frost may be induced on the surface of thesemiconductor device module. Even when the semiconductor device modulehas been cooled down under the influence of the refrigeration system,the semiconductor device module can rapidly be heated by receiving heatfrom the heater. Since the rise in temperature can be accelerated by theheater as compared with the natural radiation of heat, the working timeof replacement or maintenance can remarkably be shortened. The heatermay be attached to the heat transfer plate disposed between the dryevaporator and the printed circuit board.

[0054] When the heater of the aforementioned type is employed, a thermalsensor is preferably mounted on the printed circuit board. The thermalsensor can be utilized to prevent an excessive rise in temperature bythe heater, for example. Based on the temperature detected by thethermal sensor, the operation of the heater can reliably be terminatedbefore the printed circuit board actually suffers from an excessive risein temperature.

[0055] In general, any of the aforementioned semiconductor devicemodules may be received on a large-sized printed circuit board. Aconnector may be mounted on the large-sized printed circuit board so asto hold the semiconductor device module on the large-sized printedcircuit board. When the prevention of condensation and/or frost on thesurface of the input/output pin is intended in the aforementionedmanner, such a connector for a semiconductor device module may comprise:an electric conductive member receiving an input/output pin protrudingfrom the semiconductor device module; and a heater disposed to surroundthe electric conductive member.

[0056] When the aforementioned refrigeration system is intentionallyemployed to cool the semiconductor device module, a semiconductor deviceenclosure unit may be prepared to include a box-shaped enclosuredesigned to contain a dry evaporator contacting a semiconductor elementon a printed circuit board; and a dehumidifier designed to releasemoisture from a closed space defined in the box-shaped enclosure to anopen space outside the box-shaped enclosure.

[0057] When the dehumidifier serves to release moisture toward the openspace outside the semiconductor device enclosure unit, a dry atmospherecan be established within the box-shaped enclosure. The dry atmosphereserves to lower the dew point of the vapor included in the air.Accordingly, condensation and/or frost can reliably be prevented on thesurfaces of the printed circuit board, the semiconductor element and thedry evaporator within the box-shaped enclosure.

[0058] In this case, a heater may be attached to the inner surface ofthe box-shaped enclosure. The heater may be utilized when thesemiconductor element is to be replaced or maintained. The heat from theheater serves to heat the atmosphere within the box-shaped enclosure.When the atmosphere in the box-shaped enclosure is heated, a rise intemperature can be established on the inner surface of the box-shapedenclosure and the surface of the printed circuit board. If the innersurface of the box-shaped enclosure and the surface of the printedcircuit board are exposed to an exterior atmosphere of a roomtemperature after the atmosphere has been heated within the box-shapedenclosure in the aforementioned manner, it is possible to preventcondensation on the inner surface of the box-shaped enclosure and thesurface of the printed circuit board. Since the rise in temperature canbe accelerated as compared with the natural radiation of heat, theworking time of replacement or maintenance can remarkably be shortened.

[0059] Otherwise, a semiconductor device enclosure unit may comprise: afirst box-shaped enclosure designed to contain a dry evaporatorcontacting a semiconductor element on a printed circuit board; a secondbox-shaped enclosure designed to contain the first box-shaped enclosure;a first dehumidifier designed to release moisture from a closed spacedefined in the first box-shaped enclosure to an outside; and a seconddehumidifier designed to release moisture from a closed space within thesecond box-shaped enclosure to an open space outside the secondbox-shaped enclosure. The semiconductor device enclosure unit of thistype serves to further efficiently release moisture in the vicinity ofthe printed circuit board outward to the open space. Even when theatmosphere in the first box-shaped enclosure reaches a cryogenictemperature, it is still possible to reliably prevent condensationand/or frost within the first box-shaped enclosure. In this case, theaforementioned heater may be attached at least to the inner surface ofthe first box-shaped enclosure.

[0060] Furthermore, a semiconductor device module may comprise: aprinted circuit board; a semiconductor element mounted on the printedcircuit board; a casing attached to the printed circuit board anddesigned to define a refrigerant passage; and a cooling elementextending across the refrigerant passage and designed to protrude itstip end out of the casing. The tip end is allowed to contact thesemiconductor element. In this semiconductor device module, the coolingelement serves to transfer heat, generated at the semiconductor element,to the refrigerant in an efficient manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The above and other objects, features and advantages of thepresent invention will become apparent from the following description ofthe preferred embodiments in conjunction with the accompanying drawings,wherein:

[0062]FIG. 1 schematically illustrates the structure of a large-sizedcomputer incorporating a refrigeration system of a closed cycleaccording to a first embodiment of the present invention;

[0063]FIG. 2 is a graph illustrating a heat transfer coefficient of arefrigerant;

[0064]FIG. 3 is an enlarged sectional view illustrating a dry evaporatoraccording to a specific example;

[0065]FIG. 4 is a plan view of a bottom plate for illustrating thestructure of fins within a vaporization chamber;

[0066]FIG. 5 is a plan view of a bottom plate for illustrating thestructure of fins according to another specific example;

[0067]FIG. 6 is a plan view of a bottom plate for illustrating thestructure of fins according to a further specific example;

[0068]FIG. 7 is a sectional view illustrating the structure of a dryevaporator according to another specific example;

[0069]FIG. 8 is a plan view of an intermediate plate of the dryevaporator;

[0070]FIG. 9 is a sectional view illustrating the structure of a dryevaporator according to a modification of the specific example shown inFIG. 7;

[0071]FIG. 10 is a sectional view illustrating the structure of a dryevaporator according to another modification of the specific exampleshown in FIG. 7;

[0072]FIG. 11 is a plan view illustrating an intermediate plate of thedry evaporator;

[0073]FIG. 12 is a plan view of an intermediate plate for illustratingthe structure of a refrigerant introduction chamber and a refrigerantdischarge chamber;

[0074]FIG. 13 is a plan view of an intermediate plate for illustratingthe structure of a refrigerant introduction chamber and a refrigerantdischarge chamber;

[0075]FIG. 14 is a plan view of an intermediate plate for illustratingthe structure of a refrigerant introduction chamber and a refrigerantdischarge chamber;

[0076]FIG. 15 is a sectional view illustrating the structure of a dryevaporator according to a further specific example;

[0077]FIG. 16 is a plan view of an intermediate plate for illustratingthe structure of a refrigerant introduction chamber and a refrigerantdischarge chamber in the dry evaporator shown in FIG. 15;

[0078]FIG. 17 is a sectional view of the dry evaporator for illustratingthe concept of a gas-liquid separation within the vaporization chamber;

[0079]FIG. 18 is a sectional view illustrating the dry evaporatoraccording to a specific example for the gas-liquid separation;

[0080]FIG. 19 is a plan view of a heat transfer plate for illustratingthe dry evaporator according to the specific example shown in FIG. 18;

[0081]FIG. 20 is a sectional view illustrating the dry evaporatoraccording to a modification of the specific example shown in FIGS. 18and 19;

[0082]FIG. 21 is a sectional view illustrating the dry evaporatoraccording to another modification of the specific example shown in FIGS.18 and 19;

[0083]FIG. 22 is a sectional view illustrating the semiconductor devicemodule according to a specific example;

[0084]FIG. 23 is a sectional view illustrating the semiconductor devicemodule according to a modification of the specific example;

[0085]FIG. 24 is a sectional view illustrating the semiconductor devicemodule according to another specific example;

[0086]FIG. 25 is an enlarged partial view illustrating a film heateraccording to a specific modified example;

[0087]FIG. 26 is an enlarged partial view illustrating a film heateraccording to another specific modified example;

[0088]FIG. 27 is an enlarged sectional view partly illustrating a filmheater according to a further specific modified example;

[0089]FIG. 28 is an enlarged sectional view illustrating a bolt forfixation;

[0090]FIG. 29 is a side view illustrating the semiconductor devicemodule according to a further specific example;

[0091]FIG. 30 is a plan view of the dry evaporator for illustrating theshape of a heater;

[0092]FIG. 31 is a sectional view illustrating the semiconductor devicemodule according to a still further specific example;

[0093]FIG. 32 is a sectional view, of the heat transfer plate, takenalong the line 32-32 in FIG. 31;

[0094]FIG. 33 is an enlarged sectional view of the semiconductor deviceenclosure unit for illustrating the dehumidifier according to a specificexample;

[0095]FIG. 34 is an enlarged sectional view of the semiconductor deviceenclosure unit according to another specific example;

[0096]FIG. 35 is an enlarged sectional view of the semiconductor deviceenclosure unit according to a further specific example;

[0097]FIG. 36 is an enlarged sectional view of the semiconductor deviceenclosure unit according to a modification of the further specificexample;

[0098]FIG. 37 is an enlarged sectional view of the semiconductor deviceenclosure unit according to another modification of the further specificexample;

[0099]FIG. 38 is an enlarged sectional view of the semiconductor deviceenclosure unit according to a further modification of the furtherspecific example;

[0100]FIG. 39 schematically illustrates the structure of a refrigerationsystem of a closed cycle according to a second embodiment of the presentinvention;

[0101]FIG. 40 is an enlarged sectional view illustrating a switchingvalve;

[0102]FIG. 41 is an enlarged sectional view illustrating the switchingvalve;

[0103]FIG. 42 schematically illustrates the structure of a refrigerationsystem of a closed cycle according to a second embodiment of the presentinvention;

[0104]FIG. 43 is an enlarged partial plan view of the heat transferplate for illustrating the structure of a fin aggregate within thevaporization chamber;

[0105]FIG. 44 is a sectional perspective view taken along the line 44-44in FIG. 43;

[0106]FIG. 45 is a sectional perspective view illustrating the finaggregate according to another specific example;

[0107]FIG. 46 is a sectional perspective view illustrating the finaggregate according to a further specific example;

[0108]FIG. 47 is an enlarged perspective view illustrating the structureof a dry evaporator comprising a cooling element or piston;

[0109]FIG. 48 is a sectional partial view of the dry evaporator forillustrating the structure of pistons;

[0110]FIG. 49 is a plan view schematically illustrating the structure ofa refrigerant passage within the casing;

[0111]FIG. 50 is a plan view schematically illustrating the structure ofa refrigerant passage according to another specific example;

[0112]FIG. 51 is a sectional partial view of the dry evaporator forillustrating the structure of pistons according to another specificexample;

[0113]FIG. 52 is a plan view of the dry evaporator for illustrating thestructure of fins attached to the pistons;

[0114]FIG. 53 is a sectional view of the dry evaporator forschematically illustrating pistons incorporated within a block member;

[0115]FIG. 54 is an enlarged perspective view schematically illustratingthe structure of the piston;

[0116]FIG. 55 is an enlarged perspective view schematically illustratingthe structure of a piston according to a modification of the exampleshown in FIG. 54;

[0117]FIG. 56 is an enlarged perspective view schematically illustratingthe structure of a piston according to another specific example;

[0118]FIG. 57 is a sectional view of the dry evaporator forschematically illustrating structure of a connecting hole formed in thepiston;

[0119]FIGS. 58A to 58C are sectional views of the piston forschematically illustrating process of forming the connecting hole;

[0120]FIG. 59 is an enlarged perspective view schematically illustratingthe structure of a piston according to a further =specific example;

[0121]FIG. 60 is a sectional view of the dry evaporator forschematically illustrating the flow of the refrigerant;

[0122]FIG. 61 is an enlarged perspective view schematically illustratingthe structure of a piston according to a still further specific example;

[0123]FIG. 62 is a sectional view of the dry evaporator forschematically illustrating the flow of the refrigerant;

[0124]FIG. 63 is an enlarged perspective view schematically illustratingthe structure of a piston according to a still further specific example;

[0125]FIG. 64 is a sectional view of the dry evaporator forschematically illustrating the flow of the refrigerant;

[0126]FIG. 65 is a block diagram schematically illustrating thestructure of an air-purge mechanism;

[0127]FIG. 66 is a block diagram schematically illustrating thestructure of the air-purge mechanism set in the activation mode; and

[0128]FIG. 67 schematically illustrates the structure of a refrigerationsystem of a closed cycle according to a fourth embodiment of the presentinvention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0129]FIG. 1 schematically illustrates the structure of a large-sizedcomputer 10, such as a main frame or the like. The large-sized computer10 includes one or more large-sized printed circuit boards 11, forexample. One or more semiconductor device modules 12 such as MCMs(multichip modules) are mounted on the surface of the printed circuitboard 11. One or more memory chips or modules, not shown, likewisemounted on the surface of the printed circuit board 11, may electricallybe connected to the semiconductor device module 12. As conventionallyknown, the semiconductor device module 12 includes a small-sized printedcircuit board and one or more semiconductor chips or elements mounted onthe small-sized printed circuit board. The semiconductor element can berepresented by an LSI (large-scale integrated circuit) chip and thelike, for example. The individual semiconductor device module 12 mayfunction as a single CPU (central processing unit). Otherwise, anycombination of the semiconductor device modules 12 can be utilized toestablish a single CPU.

[0130] A refrigeration system 13 of a closed cycle according to a firstembodiment of the present invention is connected or coupled to thelarge-sized printed circuit board 11. The refrigeration system 13 isprovided with a circulation channel 14 through which a refrigerant of alow boiling point, such as an HFC (R-404A), is allowed to circulate. Acompressor 15 is incorporated in the circulation channel 14 fordischarging the refrigerant of gas state, namely, a refrigerant gasunder a high pressure such as 15 atm, for example. An oil separator 16is connected to the discharge port of the compressor 15 downstream ofthe compressor 15. The oil separator 16 is designed to separate the oilincluded in the refrigerant gas discharged out of the compressor 15. Theseparated oil is returned to the compressor 15. As conventionally known,the oil serves as a lubricating agent within the compressor 15.

[0131] A condenser 17 is incorporated in the circulation channel 14downstream of the oil separator 16. The condenser 17 is designed toallow the refrigerant gas, supplied from the compressor 15, to condenseinto the refrigerant of liquid state, namely, a refrigerant liquid. Therefrigerant liquid is supplied to a receiver 18 incorporated in thecirculation channel 14 downstream of the condenser 17. A ventilation fan19 or the like may be employed to promote heat radiation from thecondenser 17, for example.

[0132] An expansion valve 21 as a flow controller is incorporated in thecirculation channel 14 downstream of the receiver 18. The expansionvalve 21 is designed to discharge the refrigerant liquid under a lowpressure. Rapid reduction in pressure induces reduction in thetemperature of the refrigerant liquid. The resulting low pressure alsoleads to a low boiling or vaporization temperature of the refrigerantliquid.

[0133] A dry evaporator 22 is incorporated in the circulation channel 14downstream of the expansion valve 21. The dry evaporator 22 is designedto contact a target heating object, namely, the semiconductor element onthe semiconductor device module 12. A quality controller or subsidiaryevaporator 23 is incorporated in the circulation channel 14 downstreamof the dry evaporator 22. The function of the dry and subsidiaryevaporators 22, 23 will be described later in detail. An accumulator 24is connected to the subsidiary evaporator 23 downstream of thesubsidiary evaporator 23. As conventionally known, the accumulator 24 isdesigned to convert the refrigerant of liquid state, namely, therefrigerant liquid, erroneously discharged out of the subsidiaryevaporator 23 into the refrigerant of gas state, namely, the refrigerantgas. In this manner, the compressor 15 is only allowed to receive therefrigerant gas. The accumulator 24 thus serves to prevent thecompression of liquid in the compressor 15.

[0134] In addition, the circulation channel 14 may incorporate astrainer 26 and an observation window 27. The strainer 26 is designed toremove moisture, dust, and the like, from the refrigerant discharged outof the receiver 18. An operator may utilize the observation window 27 soas to visually observe the condition of the refrigerant circulating inthe circulation channel 14. Optionally, a check valve, not shown, may beincorporated in the circulation channel 14.

[0135] A thermal insulator 28 is wrapped around the circulation channel14 extending from the expansion valve 21 to the compressor 15. Thethermal insulator 28 is designed to prevent a ductwork for thecirculation channel 14 and the outer surface of the dry evaporator 22from suffering from condensation and/or frost.

[0136] A semiconductor device enclosure unit 31 is disposed within ahousing 30 of the large-sized computer 10. The enclosure unit 31 isdesigned to define a dry space, namely, a low dew point chamber inside.The enclosure unit 31 may include a box-shaped enclosure 32 airtightlycontaining the large-sized printed circuit board 11 and the dryevaporator 22 closely contacting the semiconductor element on thelarge-sized printed circuit board 11, and a dehumidifier 33 attached tothe box-shaped enclosure 32. A detailed description will be made lateron the dehumidifier 33. The dehumidifier 33 serves to establish the dryspace within the box-shaped enclosure 32.

[0137] As is apparent from FIG. 1, couplers 34 may be employed toconnect the section of the circulation channel 14 within thesemiconductor device enclosure unit 31 and the section of thecirculation channel 14 outside the enclosure unit 31. The couplers 34serve to allow separation between the sections within and outside theenclosure unit 31 in the circulation channel 14. It is preferable that aself-sealing mechanism such as a mechanical seal, for example, isassembled within the respective couplers 34. The self-sealing mechanismserves to prevent air and/or other undesirable substances from enteringthe circulation channel 14 even when the connections of the couplers 34have been released.

[0138] Here, description will be made on the operation of therefrigeration system 13. During the operation of the refrigerationsystem 13, the compressor 15 serves to induce the circulation of arefrigerant through the circulation channel 14. The refrigerant ismaintained at a higher pressure in the circulation channel 14 startingfrom the compressor 15 so as to reach the expansion valve 21. In thissituation, the refrigerant may have the vaporization temperature orboiling point at approximately 40 degrees Celsius, for example. On theother hand, the refrigerant is maintained at a lower pressure in thecirculation channel 14 starting from the expansion valve 21 so as toreturn to the compressor 15. If the refrigerant is maintained at a lowerpressure, the vaporization temperature of the refrigerant can be loweredto the level at approximately −20 degrees Celsius, for example.Accordingly, the vaporization of the refrigerant can be promoted at alower pressure. Environmental or surrounding heat energy can be absorbedinto the refrigerant in response to the vaporization.

[0139] The dry evaporator 22 receives the refrigerant at a quality of arange between 0.3-0.5. At the dry evaporator 22, the refrigerant ispromoted to evaporate by receiving a heat energy from the semiconductorelement. In this case, the quality of the refrigerant within the dryevaporator 22 is maintained at a level below 1.0, for example, at alevel below approximately 0.85. In other words, the dry evaporator 22 isdesigned to discharge the refrigerant of the quality smaller than 0.85,namely, of gas-liquid mixture state. The quality established in the dryevaporator 22 can be adjusted based on the amount of heat generation atthe target heating object or semiconductor element and the flow orcurrent of the refrigerant introduced into the dry evaporator 22, asconventionally known. The flow or current of the refrigerant can becontrolled by the discharge amount of the compressor 15 and the openingdegree of the expansion valve 21.

[0140] The subsidiary evaporator 23 applies heat to the refrigerant ofgas-liquid mixture state discharged out of the dry evaporator 22. Theheat may be generated by the operation of a heater, for example. Theapplied heat serves to cause the refrigerant of liquid state, namely,the remaining refrigerant liquid to evaporate. After the quality of 1.0has been achieved, the refrigerant of gas state is discharged out of thesubsidiary evaporator 23. The quantity of the applied heat energy in thesubsidiary evaporator 23 can be determined based on the quality and theflow or current of the refrigerant introduced into the subsidiaryevaporator 23, for example.

[0141] As is apparent from FIG. 2, the heat transfer coefficient, or thequantity of the heat transfer per unit area, of the refrigerant dependson the quality. In this specific example, the heat transfer coefficientof the refrigerant remarkably drops when the quality of the refrigerantexceeds 0.85. Accordingly, if the quality of the refrigerant ismaintained at a level below 0.85 in the dry evaporator 22 directlycontacting the target heating object, the dry evaporator 22 is allowedto accomplish a higher performance of cooling. Even when the refrigerantof gas-liquid state is discharged out of the dry evaporator 22 in theaforementioned manner, the subsidiary evaporator 23 serves to fullyevaporate the remaining refrigerant liquid, so that the compressor 15can reliably be prevented from a compression of a refrigerant liquidwithout increasing a load to the accumulator 24. If a refrigerant liquidcompletely evaporates in a dry evaporator in a conventional manner, theheat transfer coefficient of the refrigerant remarkably drops after thequality of the refrigerant exceeds 0.85. Specifically, the conventionaldry evaporator is forced to absorb the heat from the target heatingobject or semiconductor element at a lower heat transfer coefficient. Ascompared with the dry evaporator 22 of the invention, only a lowerperformance of cooling can be obtained in the conventional dryevaporator. It should be noted that the quality of the refrigerant,other than 0.85, can be set in an appropriate manner in theaforementioned dry evaporator 22 of the invention based on the kind of arefrigerant and the capability of cooling required in the dry evaporator22.

[0142] Next, a detailed description will be made on the structure of thedry evaporator 22. As shown in FIG. 3, for example, the dry evaporator22 includes a casing 41. The casing 41 comprises a heat transfer orbottom plate 42 extending in a horizontal direction, and a top plate 43extending in parallel with the bottom plate 42. The bottom plate 42 isdesigned to contact the semiconductor element on the semiconductordevice module 12. A closed space or vaporization chamber 44 in the formof a rectangular parallelepiped is defined between the top and bottomplates 43, 42, for example. The casing 41 may be made from a high heatconductive material such as a copper material.

[0143] The top plate 43 is designed to receive the connection of aninlet duct 45, extending from the top plate 43 in a vertical directionso as to define a refrigerant introduction passage inside, and theconnection of an outlet duct 46, likewise extending from the top plate43 in a vertical direction so as to define a refrigerant dischargepassage inside. The inlet and outlet ducts 45, 46 are coupled to the topplate 43 through couplers 47, respectively. A refrigerant inlet 48 isdefined in the top plate 43 of the casing 41 so as to open therefrigerant introduction passage at the inner surface of thevaporization chamber 44 or the lower surface of the top plate 43.Likewise, a refrigerant outlet 49 is defined in the top plate 43 of thecasing 41 so as to open the refrigerant discharge passage at the innersurface of the vaporization chamber 44 or lower surface of the top plate43.

[0144] As is apparent from FIG. 4, a group of fins 51 is formed on thebottom plate 42 so as to protrude from the inner surface of thevaporization chamber 44 or an upper surface of the bottom plate 42. Thegroup of fins 51 is designed to define a plurality of refrigerantpassages extending in parallel from the refrigerant inlet 48 toward therefrigerant outlet 49, respectively. The respective fins 51 may beformed to stand up from the upper surface of the bottom plate 42 so asto reach the lower surface of the top plate 43 at the tip ends,respectively. The group of fins 51 serves to enlarge a heat transferarea or direct contact area between the heat transfer or bottom plate 42and the refrigerant introduced in the vaporization chamber 44, so thatheat generated at the semiconductor element on the semiconductor devicemodule 12 can efficiently be transferred to the refrigerant.

[0145] As shown in FIG. 5, assume that a straight line 52 is defined inthe vaporization chamber 44 so as to extend from the refrigerant inlet48 to the refrigerant outlet 49, for example. In this case, it ispreferable that the individual fin 51 gets shorter at a position remoterfrom the straight line 52. The fins 51 in this manner serve to provide ashorter refrigerant passage at a position remoter from the straight line52.

[0146] The refrigerant circulating through the circulation channel 14 isallowed to pass through the vaporization chamber 44 based on thepressurized or urging force applied from the compressor 15. Therefrigerant discharged out of the refrigerant inlet 48 is supposed toflow along the straight line 52 toward the refrigerant outlet 49,because the maximum pressure can be maintained along the shortest path.The remoter from the straight line 52 the refrigerant passage is locatedat, the less pressurized force can be applied to the refrigerant passingthrough the refrigerant passage. If the refrigerant passage getsshorter, the refrigerant passage may be released from a larger loss ofthe applied pressure. The shorter refrigerant passage at a positionremoter from the straight line 52 in the aforementioned manner issupposed to equally distribute the refrigerant to the respectiverefrigerant passages defined between the adjacent fins 51. A higherperformance of cooling for the semiconductor element on thesemiconductor device module 12 can uniformly be established in theoverall vaporization chamber 44.

[0147] In place of the aforementioned shorter refrigerant passage at alocation remoter from the straight line 52, a refrigerant passage mayget wider at a position remoter from the straight line 52, as shown inFIG. 6, for example. The wider refrigerant passage is supposed to reducea larger loss of the applied pressure, so that the refrigerant isequally distributed to the respective refrigerant passages definedbetween the adjacent fins 51 in the same manner as the aforementionedexample. A higher performance of cooling for the semiconductor elementon the semiconductor device module 12 can uniformly be established inthe overall vaporization chamber 44.

[0148]FIG. 7 illustrates the structure of the dry evaporator 22according to another specific example. The dry evaporator 22 includes acasing 53. The casing 53 comprises a bottom plate 54 extending in ahorizontal direction, and a top plate 55 extending in parallel with thebottom plate 54. The bottom plate 54 is designed to contact thesemiconductor element on the semiconductor device module 12. A closedspace in the form of a rectangular parallelepiped is defined between thetop and bottom plates 54, 55, for example. First and second side walls56, 57 are designed to stand upright on the bottom plate 54 on theopposite sides of the closed space. The first and second side walls 56,57 reach the top plate 55 at their top ends, respectively. Anintermediate or partition plate 58 is disposed between the top andbottom plates 55, 54 within the closed space. The intermediate plate 58is designed to extend in parallel with the bottom plate 54. Avaporization chamber 59 is defined between the intermediate and bottomplates 58, 54. The casing 53 may be made from a high heat conductivematerial such as a copper material.

[0149] A partition wall 60 is disposed within the closed space betweenthe intermediate and the top plates 58, 55. The partition wall 60 isdesigned to extend in parallel with the first and second side walls 56,57 between the first and second side walls 56, 57. The partition wall 60serves to define a refrigerant introduction chamber adjacent the firstside wall 56 and a refrigerant discharge chamber 62 adjacent the secondside wall 57 between the intermediate and top plates 58, 55.

[0150] The top plate 55 is designed to receive the connection of aninlet duct 63, extending from the top plate 55 in a vertical directionso as to define a refrigerant introduction passage inside, and theconnection of an outlet duct 64, likewise extending from the top plate55 in a vertical direction so as to define a refrigerant dischargepassage inside. The inlet and outlet ducts 63, 64 are coupled to the topplate 55 through couplers 65, respectively. A refrigerant inlet 66 isdefined in the top plate 55 of the casing 53 at a location adjacent thepartition wall 60 so as to open the refrigerant introduction passage atthe inner surface of the refrigerant introduction chamber 61 or thelower surface of the top plate 55. Likewise, a refrigerant outlet 67 isdefined in the top plate 55 of the casing 53 at a location adjacent thepartition wall 60 so as to open the refrigerant discharge passage at theinner surface of the refrigerant discharge chamber 62 or the lowersurface of the top plate 55.

[0151] As is apparent from FIG. 8, an introduction opening 68 is definedbetween the first side wall 56 and the peripheral edge of theintermediate plate 58. The introduction opening 68 serves to connect theupper refrigerant introduction chamber 61 and the lower vaporizationchamber 59 to each other. In this manner, the refrigerant introductionchamber 61 is allowed to extend from the refrigerant inlet 66 to thevaporization chamber 59. On the other hand, a discharge opening 69 islikewise defined between the second side wall 57 and the peripheral edgeof the intermediate plate 58. The discharge opening 69 serves to connectthe upper refrigerant discharge chamber 62 and the lower vaporizationchamber 59 to each other. In this manner, the refrigerant dischargechamber 62 is allowed to extend from the vaporization chamber 59 to therefrigerant outlet 67.

[0152] A refrigerant is introduced into the refrigerant introductionchamber 61 from the inlet duct 63 through the refrigerant inlet 66 inthis dry evaporator 22. The introduced refrigerant flows along theintermediate plate 58 so as to enter the vaporization chamber 59 throughthe introduction opening 68. The refrigerant in the vaporization chamber59 is allowed to receive or absorb heat of the semiconductor devicemodule 12 via the heat transfer or bottom plate 54. The semiconductordevice module 12 is thus cooled down.

[0153] The refrigerant of a higher quality is led to the refrigerantdischarge chamber 62 through the discharge opening 69. The refrigerantthen flows along the intermediate plate 58 into the refrigerant outlet67. The refrigerant flowing out of the refrigerant outlet 67 ismaintained at a temperature lower than that of the refrigerant flowingthrough the refrigerant inlet 66. The intermediate plate 58 is allowedto achieve a heat exchange between the refrigerants in the refrigerantinlet and outlet 66, 67 based on the difference in temperature. It ispossible to restrain variation in the quality of the refrigerant headedtoward the vaporization chamber 59 from the refrigerant inlet 66. Astill higher performance of cooling can be achieved in the dryevaporator 22.

[0154] As shown in FIG. 8, a plurality of fins 70 may integrally beformed on the intermediate plate 58 so as to define a plurality ofrefrigerant passages crossing the refrigerant introduction chamber 61from the refrigerant inlet 66 to the introduction opening 68. Likewise,a plurality of fins 71 may integrally be formed on the intermediateplate 58 so as to define a plurality of refrigerant passages crossingthe refrigerant discharge chamber 62 from the discharge opening 69 tothe refrigerant outlet 67. The fins 70, 71 are expected to promote theaforementioned heat exchange between the refrigerants in the refrigerantinlet and outlet 66, 67. In addition, a plurality of fins 72 mayintegrally be formed on the bottom plate 54, as shown in FIG. 7. Thefins 72 are designed to define a plurality of refrigerant passagesextending in parallel from the introduction opening 68 and the dischargeopening 69. The fins 72 serve to efficiently transfer heat of thesemiconductor element on the semiconductor device module 12 to therefrigerant. If the fins 72 are allowed to reach the intermediate plate58 at the top ends, the aforementioned heat exchange between therefrigerants may further be promoted.

[0155] For example, the refrigerant introduction chamber 61 and/or therefrigerant discharge chamber 62 in the dry evaporator 22 may be dividedinto a plurality of cumulative or piled chambers, as shown in FIG. 9.First and second subsidiary intermediate or partition plates 73, 74 canbe employed to achieve such division. The first and second subsidiaryintermediate plates 73, 74 are designed to extend between theintermediate plate 58 and the top plate 55 in parallel with the bottomplate 54. The first and second subsidiary intermediate plates 73, 74 aresupposed to further improve a heat exchange between the refrigerantflowing through the refrigerant inlet 66 and the refrigerant flowingthrough the refrigerant outlet 67.

[0156]FIGS. 10 and 11 illustrates the dry evaporator 22 according to amodification of the aforementioned specific example. The space betweenthe top and intermediate plates 55, 58 is set smaller than the spacebetween the bottom and intermediate plates 54, 58 in this dry evaporator22. The smaller space between the top and intermediate plates 55, 58 isexpected to accelerate the loss or consumption of pressure for therefrigerant in the refrigerant introduction chamber 61, so that therefrigerant liquid can be prevented from vaporization to the utmostbefore it is introduced into the vaporization chamber 59. A still higherperformance of cooling can be achieved in the dry evaporator 22.

[0157] In this case, it is preferable that a dike 75 is formed on theintermediate plate 58 so as to swell from the upper surface of theintermediate plate 58. The dike 75 is designed to extend along the edgeof the intermediate plate 58 at a location adjacent the introductionopening 68. The dike 75 serves to reliably promote an accelerated lossor consumption of pressure for the refrigerant in the refrigerantintroduction chamber 61. The refrigerant liquid is still reliablyprevented from vaporization. Moreover, the dike 75 is also expected toallow a uniform inflow of the refrigerant over the entire introductionopening 68, so that the refrigerant can uniformly be distributed intothe respective refrigerant passages within the vaporization chamber 59.

[0158] In addition, the refrigerant introduction chamber 61 may bedesigned to by degree expand as it gets closer to the introductionopening 68, namely, the vaporization chamber 59, as shown in FIG. 12,for example. The refrigerant introduction chamber 61 of this type isexpected to reliably making a uniform inflow of the refrigerant over theentire introduction opening 68. The refrigerant can uniformly bedistributed into the respective refrigerant passages in theaforementioned manner. Moreover, the refrigerant discharge chamber 62may be designed to by degree narrow as it gets closer to the refrigerantoutlet 67. The refrigerant discharge chamber 62 of this type alsocontributes to a uniform distribution of the refrigerant into therespective refrigerant passages in the vaporization chamber 59. Thegradually expanded refrigerant introduction chamber 61 and/or thegradually narrowed refrigerant discharge chamber 62 may be formed bysimply defining a curved surface on the inner surface of the refrigerantintroduction and discharge chambers 61, 62, as is apparent from FIG. 12.

[0159] As shown in FIG. 13, a plurality of refrigerant passages 76 maybe defined within the refrigerant introduction chamber 61 so as torespectively extend from the refrigerant inlet 66 to the introductionopening 68, namely, the vaporization chamber 59, for example. Therefrigerant passages 76 serve to uniformly distribute the refrigerant tothe respective refrigerant passages in the vaporization chamber 49. Inthis case, a plurality of refrigerant passages 77 may likewise bedefined within the refrigerant discharge chamber 62 so as torespectively extend from the vaporization chamber 59, namely, thedischarge opening 69 to the refrigerant outlet 67, as is apparent fromFIG. 13, for example. The refrigerant passages 77 also contribute to auniform distribution of the refrigerant into the respective refrigerantpassages in the vaporization chamber 59.

[0160] If the refrigerant passages 76 are defined within the refrigerantintroduction chamber 61 in this manner, an expanded passage 78 may beconnected to the downstream end of the individual refrigerant passage76, as shown in FIG. 14, for example. The individual refrigerant passage76 is connected to the lower vaporization chamber 59 through theexpanded passage 78. The expanded passage 78 serves to remarkablyincrease the loss of pressure for the refrigerant, so that thevaporization of the refrigerant flowing into the vaporization chamber 59can be promoted. A performance of cooling can be improved in the dryevaporator 22.

[0161]FIGS. 15 and 16 illustrates the structure of the dry evaporator 22according to a further specific example. The dry evaporator 22 includesa casing 81. The casing 81 comprises a bottom plate 82 extending in ahorizontal direction, and a top plate 83 extending in parallel with thebottom plate 82. The bottom plate 82 is designed to contact thesemiconductor element on the semiconductor device module 12. A closedspace in the form of a rectangular parallelepiped is defined between thetop and bottom plates 82, 83, for example. The closed space issurrounded by a side wall 84. The side wall 84 is designed to standupright on the upper surface of the bottom plate 82 and reach the topplate 83 at its top end. An intermediate or partition plate 85 isdisposed between the top and bottom plates 83, 82 within the closedspace. The intermediate plate 85 is designed to extend in parallel withthe bottom plate 82. A vaporization chamber 86 is defined between theintermediate and bottom plates 85, 82. On the other hand, a refrigerantdischarge chamber 87 is likewise defined between the intermediate andtop plates 85, 83. The casing 81 may be made from a high heat conductivematerial such as a copper material.

[0162] An inlet duct 88 is connected to the intermediate plate 85. Theinlet duct 88 is designed to extend in a vertical direction. The inletduct 88 is utilized to define a refrigerant introduction passage whichpenetrates through the refrigerant discharge chamber 87 so as to reachthe vaporization chamber 86. The inlet duct 88 may be made from a highheat conductive material such as a copper material. An outlet duct 89extending in a vertical direction is likewise connected to the top plate83. The outlet duct 89 is designed to define a refrigerant dischargepassage extending from the refrigerant discharge chamber 87. Therefrigerant discharge passage surrounds the inlet duct 88. Referringalso to FIG. 16, a discharge opening is defined between the edge of theintermediate plate 85 and the side wall 84 so as to connect the lowervaporization chamber 86 and the upper refrigerant discharge chamber 87.

[0163] A refrigerant is introduced in the vaporization chamber 86through the refrigerant introduction passage defined within the inletduct 88 in the aforementioned dry evaporator 22. The refrigerant in thevaporization chamber 86 is allowed to receive or absorb heat of thesemiconductor device module 12 via the heat transfer or bottom plate 82.The semiconductor device module 12 is thus cooled down.

[0164] The refrigerant of a higher quality is led to the upperrefrigerant discharge chamber 87 from the lower vaporization chamber 86.The refrigerant then flows out through the refrigerant discharge passagedefined between the inner surface of the outlet duct 89 and the outersurface of the inlet duct 88. In this situation, the refrigerant flowingthrough the refrigerant discharge passage is maintained at a temperaturelower than that of the refrigerant flowing through the refrigerantintroduction passage. The wall of the inlet duct 88 serves to establisha heat exchange between the refrigerants in the refrigerant dischargeand introduction passages based on the difference in temperature. It isthus possible to restrain variation in the quality of the refrigerantheaded toward the vaporization chamber 86 from the refrigerantintroduction passage. A higher performance of cooling can be achieved inthe dry evaporator 22.

[0165] For example, the dry evaporator 22 shown in FIG. 3 may accomplisha gas-liquid separation of the refrigerant in the vaporization chamber44. The gas-liquid separation can be achieved based on the flow orcurrent of the refrigerant discharged from a flow or current controllersuch as the expansion valve 21. In this case, the refrigerant of liquidstate, namely, the refrigerant liquid runs along the upper surface ofthe bottom plate 42 under the influence of the gravity in thevaporization chamber 44, as shown in FIG. 17, for example. On the otherhand, the refrigerant of gas state, namely, the refrigerant gas receivesa smaller influence of the gravity, so that the refrigerant gas isallowed to flow along the lower surface of the top plate 43. If thegas-liquid separation can be achieved in this manner, the refrigerantliquid is allowed to uniformly spread over the entire upper surface ofthe heat transfer or bottom plate 42, so that a higher performance ofcooling can be achieved uniformly over the broader area of the bottomplate 43.

[0166] In particular, it is preferable that the dry evaporator 22 isdesigned to have a larger sectional area in the vaporization chamber 44,as is apparent from FIG. 17, if the gas-liquid separation is intended inthe aforementioned manner. The larger sectional area of the vaporizationchamber 44 can be achieved by enlarging the space H1, defined betweenthe bottom and top plates 42, 43, to the space H2, for example. Here,the sectional area of the vaporization chamber 44 is measured based on aprofile in a plane perpendicular to the direction of the flow or currentof the refrigerant.

[0167] When the aforementioned gas-liquid separation is intended, thedry evaporator 22 may include a casing 93 comprising a vertical heattransfer plate 92 designed to contact a target heating object such asthe semiconductor device module 12, as shown in FIG. 18, for example. Aclosed space or vaporization chamber 95 in the form of a parallelepipedis defined between the heat transfer plate 92 and a back plate 94extending in parallel with the heat transfer plate 92 in this casing 93.The vaporization chamber 95 is allowed to extend in a vertical directionalong the heat transfer plate 92 from a bottom plate 96 upright to theheat transfer plate 92. The bottom plate 96 is designed to extend in ahorizontal direction from the heat transfer plate 96 so as to reach theback plate 94 at the tip end. The casing 93 may be made from a high heatconductive material such as a copper material, for example.

[0168] The back plate 94 is designed to receive the connection of aninlet duct 97, extending in a horizontal direction so as to define arefrigerant introduction passage inside, and the connection of an outletduct 98, likewise extending in a horizontal direction so as to define arefrigerant discharge passage inside. The inlet and outlet ducts 97, 98are coupled to the back plate 94 through couplers 99, respectively. Arefrigerant inlet 101 is defined in the back plate 94 of the casing 93so as to open the refrigerant introduction passage at the inner surfaceof the vaporization chamber 95. Likewise, a refrigerant outlet 102 isdefined in the back plate 94 so as to open the refrigerant dischargepassage at the inner surface of the vaporization chamber 95. Therefrigerant outlet 102 is located at a position above the refrigerantinlet 101 in a vertical direction. As is apparent from FIG. 19, aplurality of fins 103 are integrally formed on the heat transfer plate92 so as to define a plurality of refrigerant passages extending inparallel from the refrigerant inlet 101 to the refrigerant outlet 102,for example.

[0169] A refrigerant discharged from the refrigerant inlet 101 isallowed to flow upward within the vaporization chamber 95 along the heattransfer plate 92 and to finally reach the refrigerant outlet 102. Ifthe gas-liquid separation is realized in the vaporization chamber 95,the refrigerant liquid falls on the upper surface of the bottom plate 96under the influence of the gravity. The refrigerant liquid received onthe bottom plate 96 can uniformly be distributed into the respectiverefrigerant passages defined between the adjacent fins 103 in the dryevaporator 22.

[0170] As shown in FIG. 20, the dry evaporator 22 may further include abypass duct 104 extending from the bottom plate 96 of the casing 93 tothe outlet duct 98, for example. The bypass duct 104 serves provide abypass channel for connecting a bypass opening 105, opened at the lowestposition within the vaporization chamber 95, and a discharge channel,such as the refrigerant discharge passage defined in the outlet duct 98,to each other. The oil from the compressor 15, which is involuntarilyintroduced in the vaporization chamber 95, received on the bottom plate96 can be led to the refrigerant discharge passage or the circulationchannel 14 through the bypass duct 104 under the influence of thedifference in pressure between the refrigerant inlet and outlet 101,102. It is possible to prevent the oil, discharged from the compressor15, from staying within the vaporization chamber 95.

[0171] When the aforementioned gas-liquid separation is intended, thedry evaporator 22 may include a casing 108 comprising a vertical heattransfer plate 107 designed to contact a target heating object such asthe semiconductor device module 12, as shown in FIG. 21, for example. Aclosed space or vaporization chamber 110 in the form of a parallelepipedis defined between the heat transfer plate 107 and a back plate 109extending in parallel with the heat transfer plate 107 in this casing108. The vaporization chamber 110 is allowed to extend in a verticaldirection along the heat transfer plate 107 from a bottom plate 111upright to the heat transfer plate 107. The bottom plate 111 is designedto extend in a horizontal direction from the heat transfer plate 107 soas to reach the back plate 109 at the tip end. The casing 108 may bemade from a high heat conductive material such as a copper material, forexample.

[0172] A partition plate 112 is disposed between the heat transfer plate107 and the back plate 109 within the upper portion of the vaporizationchamber 110 so as to extend in parallel with the heat transfer plate107. The partition plate 112 is designed to divide the upper portion ofthe vaporization chamber 110 into an introduction space 113 adjacent theheat transfer plate 107 and a discharge space 114 adjacent the backplate 109.

[0173] The back plate 109 is designed to receive the connection of aninlet duct 115, extending in a horizontal direction so as to define arefrigerant introduction passage inside, and the connection of an outletduct 116, likewise extending in a horizontal direction so as to define arefrigerant discharge passage inside. The inlet and outlet ducts 115,116 are coupled to the back plate 109 through couplers 117,respectively. A refrigerant inlet 118 is defined in the back plate 109of the casing 108 so as to open the refrigerant introduction passage atthe inner surface of the introduction space 113. Likewise, a refrigerantoutlet 119 is defined in the back plate 109 so as to open therefrigerant discharge passage at the inner surface of the dischargespace 114.

[0174] The depth D1 of the lower portion is set larger than the space D2measured between heat transfer plate 107 and the partition plate 112 inthe vaporization chamber 110. The depth Dl of the lower portion can bemeasured between the lower edge of the partition plate 112 and the uppersurface of the bottom plate 111 along a vertical direction.

[0175] A refrigerant discharged from the refrigerant inlet 118 isallowed to flow downward within the vaporization chamber 110 along theheat transfer plate 107. The refrigerant flows through the introductionspace 113 in the upper portion to the lower portion. The refrigerant isthen allowed to flow around the lower edge of the partition plate 112 soas to enter the discharge space 114 in the upper portion. Therefrigerant is thereafter discharged out of the refrigerant outlet 119.Since the depth D1 of the lower portion is set larger than the space D2between the heat transfer plate 107 and the partition plate 112, thesectional area is forced to jaggedly increase in the vaporizationchamber 110. The remarkable enlargement of the sectional area promotesthe gas-liquid separation of the refrigerant in the vaporization chamber110. Here, the sectional area of the vaporization chamber 110 ismeasured based on a profile in a plane perpendicular to the direction ofthe flow or current of the refrigerant.

[0176] The semiconductor device module 12 may be prepared to include asemiconductor element 122 such as an LSI chip mounted on the upper sideof a small-sized printed circuit board 121, as shown in FIG. 22, forexample. A plurality of semiconductor elements 122 may also be mountedin a single small-sized printed circuit board 121. A plurality ofinput/output pins 123 are designed to stand on and protrude from thelower side of the printed circuit board 121. The individual input/outputpin 123 is received in a corresponding socket bore defined in a socket124 mounted on the large-sized printed circuit board 11. The socket 124serves to hold the small-sized printed circuit board 121, namely, thesemiconductor device module 12 on the surface of the large-sized printedcircuit board 11. The socket 124 may be represented by a so-called ZIF(zero insertion force) connector, for example.

[0177] The dry evaporator 22 is fixed on the upper side of the printedcircuit board 121. Fixation is achieved with a heat insulator member 125containing the dry evaporator 22. The heat insulator member 125 servesto hold the dry evaporator 22 in contact with the upper surface of thesemiconductor element 122. Integration of the dry evaporator 22 to thesemiconductor device module 12 in this manner contributes to afacilitated attachment and detachment of the semiconductor device module12 and the dry evaporator 22 to and from the large-sized printed circuitboard 11. The operability can be improved in replacement or maintenanceof the semiconductor device module or modules 12. The heat insulatormember 125 is designed to prevent condensation and/or frost over thesurface of the dry evaporator 22.

[0178] As is apparent from FIG. 22, the heat insulator member 125 mayalso contain the input/output pins 123. In general, the metallicinput/output pins 123 are easily cooled down under the influence of theperformance of cooling by the dry evaporator 22. If the input/outputpins 123 are excessively cooled down, the surfaces of the input/outputpins 123 tend to suffer from condensation and/or frost. The input/outputpins 123 wrapped by the heat insulator member 125 can be protected fromcondensation and/or frost.

[0179] The heat insulator member 125 may be made from a foam plastic orthe like. In this case, the semiconductor element 122 is first mountedon the upper side of the small-sized printed circuit board 121. The dryevaporator 22 is then mounted on the semiconductor element 122 on theprinted circuit board 121. Thereafter, the fluid foam material isintroduced in a die to completely include the dry evaporator 22, thesemiconductor element 122 and the printed circuit board 121. When theintroduced fluid foam is hardened, the heat insulator member 125 can beobtained. The printed circuit board 121, the semiconductor element 122and the dry evaporator 22 are thus completely embedded in the heatinsulator member 125.

[0180] As is apparent from FIG. 22, the heat insulator member 125 mayalso contain film heaters 126, 127 inside in the semiconductor devicemodule 12. The input/output pins 123 may be allowed to penetrate throughthe film heater 127 so as to enter the corresponding socket boresdefined in the socket 124. The heat from the film heaters 126, 127serves to heat the heat insulator member 125. The heat from the filmheaters 126, 127 thus enables reduction in the thickness or volume ofthe heat insulator member 125, even when prevention of condensationand/or frost is intended on the surface of the dry evaporator 22. Suchreduction in the thickness of the heat insulator member 125 contributesto a higher density of the semiconductor device module 12 on thelarge-sized printed circuit board 11. The film heater 126, 127 maycomprise a cancellate or mesh-shaped heat wire unit interposed between apair of resin films, for example.

[0181] As is apparent from FIG. 22, a heat conductive film 128 may besuperposed on the film heater 126. The heat conductive film 128 isdesigned to conduct heat at a higher specific thermal conductivity. Sucha heat conductive film 128 serves to spread heat from the film heater126 over the entire area in the heat insulator member 125 even when thefilm heater 126 of a small size is employed. The heat conductive film128 may be made of a carbon film, for example.

[0182] On the other hand, a heat conductive member or film 129 may beinterposed between the dry evaporator 22 and the film heater 127, asshown in FIG. 22, for example. The heat conductive film 129 is designedto have a property allowing heat to conduct at a first specific thermalconductivity in a vertical direction oriented from the film heater 127to the dry evaporator 22, while allowing heat to conduct at a secondspecific thermal conductivity larger than the first specific thermalconductivity in a plane perpendicular to the vertical direction. Theheat conductive film 129 may be made of a carbon film, for example. Thecarbon film in general exhibits a specific thermal conductivityapproximately equal to hundredth of that of the copper in the verticaldirection and a specific thermal conductivity equal to twice thespecific thermal conductivity of the copper in the plane. The heatconductive film 129 serves to spread heat from the film heater 127 overthe entire area in the heat insulator member 125 even when the filmheater 129 of a small size is employed. Condensation and/or frost canthus reliably be prevented. Simultaneously, heat from the film heater127 can reliably be prevented from reaching the dry evaporator 22, sothat the performance of cooling in the dry evaporator 22 can solely beconcentrated on the semiconductor element 122. It is preferable that aheat insulator film 130 is interposed between the heat conductive film129 and the dry evaporator 22.

[0183] As shown in FIG. 23, for example, the heat insulator member 125may be divided into a first half piece 131 containing the small-sizedprinted circuit board 121, and a second half piece 132 containing thedry evaporator 22. The first and second half pieces 131, 132 aredetachably coupled to each other. The division into the first and secondhalf pieces 131, 132 serves to facilitate removal of the semiconductorelement 122 and the dry evaporator 22 from the small-sized printedcircuit board 121. The operability can be improved in replacement ormaintenance of the semiconductor element 122.

[0184] As shown in FIG. 24, the film heater 127 may be attached to thelower side of the small-sized printed circuit board 121. Theinput/output pins 123 are allowed to penetrate through the film heater127 so as to enter the corresponding socket bores defined in the socket124. A heat conductive film 129 may be interposed between the filmheater 127 and the printed circuit board 121. The film heater 127 and/orthe heat conductive film 129 may extend around the outer periphery ofthe printed circuit board 121, as shown in FIG. 25. Alternatively, aplurality of the film heaters 127 and the heat conductive film 129,alternately layered one another, may be attached to the printed circuitboard 121, as shown in FIG. 26. Otherwise, the film heater 127 may beattached to the socket 124, as shown in FIG. 27. The film heater 127 islocated offset to electric conductive member or pads 134 so as tosurround the individual electric conductive member or pad 134 in thesocket 124. The electric conductive members 134 are designed to receivethe corresponding input/output pins 123 in the socket 124. The electricconductive members 134 may be embedded in the corresponding socket boresin the socket 124.

[0185] As is apparent from FIG. 24, bolts 135 may be employed to fix thedry evaporator 22 to the large-sized printed circuit board 11. The boltsfor fixation may be received in a through bore 137 defined in a heattransfer plate 136 of the dry evaporator 22, as shown in FIG. 28. Thetip end of the individual bolt 135 is coupled to a corresponding screwnut 138 fixed to the large-sized printed circuit board 11. In this case,a low heat conductive member 139 is preferably interposed between theheat transfer plate 136 and the individual bolt 135. The low heatconductive member 139 serves to avoid heat transfer between the dryevaporator 22 and the large-sized printed circuit board 11 to theutmost. Accordingly, an excessive cooling of the large-sized printedcircuit board 11 can be avoided. A receiving bore 140 may be defined inthe heat insulator member 125 so as to receive the bolt 135 forfixation. The low heat conductive member 139 may be made from nylon of ahigher insulation, for example.

[0186] Otherwise, the semiconductor device module 12 may compriseheaters 142, 143 directly attached to the dry evaporator 22, as shown inFIGS. 29 and 30, for example. The heaters 142, 143 are kept in contactwith the surfaces of the dry evaporator 22 and the heat transfer plate144. The heaters 142, 143 are in general utilized when the semiconductordevice module 12 is to be removed or maintained. The heaters 142, 143may be turned on only when the operation of the refrigeration system 13is terminated. Heat from the heaters 142, 143 serves to heat the dryevaporator 22 and the heat transfer plate 143 which may have been cooledto a level below zero degrees Celsius, for example. If the semiconductordevice enclosure unit 31 is opened after the dry evaporator 22 and theheat transfer plate 144 have been heated, the dry evaporator 22, theheat transfer plate 144 and the small-sized printed circuit board 121can be prevented from condensation. Since the rise in temperature can beaccelerated by the heaters 142, 143 as compared with the naturalradiation of heat, the working time of replacement or maintenance can beshortened. The heater 143 may be embedded in the heat transfer plate144, as shown in FIGS. 31 and 32, for example.

[0187] When employment of the aforementioned heaters 142, 143 areintended, a thermal sensor 145 is preferably mounted on the small-sizedprinted circuit board 121, as shown in FIGS. 29 and 31. The thermalsensor 145 can be represented by a thermistor, for example. The thermalsensor 145 can be utilized to prevent an excessive rise in temperatureby the heaters 142, 143, for example. Based on the temperature detectedby the thermal sensor 145, the operation of the heaters 142, 143 canreliably be terminated before the small-sized printed circuit board 121suffers from an excessive rise in temperature.

[0188]FIG. 33 illustrates a specific example of the dehumidifier 33incorporated in the semiconductor device enclosure unit 31. Thehumidifier 33 includes a rotor 147 disposed within an opening 146defined in the box-shaped enclosure 32. The rotor 147 is designed torotate around a rotational shaft 148 extending across the opening 146,for example. The rotor 147 is allowed to simultaneously protrude aclosed space 149 within the box-shaped enclosure 32 and an open space150 outside the box-shaped enclosure 32. The rotor 147 may include aplurality of vanes 151 extending in the radial directions from therotational shaft 148. The respective vanes 151 may be made from adehydrator such as silica gel, zeolite, and the like, for example. A fanheater 152 may be disposed in the open space 150 outside the box-shapedenclosure 32 so as to supply a hot air to the rotor 147.

[0189] When the rotor 147 is driven to rotate, the individual vane 151is allowed to alternately enter the closed space 149 within thebox-shaped enclosure 32 and the open space 150 outside the box-shapedenclosure 32 along the circular path around the rotational shaft 148.The dehydrator of the vane 151 catches the moisture in the closed space149 within the box-shaped enclosure 32. When the vane 151 then movesinto the open space 150 outside the box-shaped enclosure 32 from theclosed space 149 within the box-shaped enclosure 32, the moisture caughtby the dehydrator can be released at the open space 150. The release ofthe moisture can be promoted by the hot air supplied from the fan heater152. The vane 151 enters the closed space 149 again after the release ofthe moisture in the open space 150.

[0190] In this manner, the individual vane 151 is allowed to passthrough the closed space 149 within the box-shaped enclosure 32 and theopen space 150 outside the box-shaped enclosure 32 alternately, so thata dry atmosphere can be maintained within the box-shaped enclosure 32.Such a dry atmosphere serves to establish a lower dew point within thebox-shaped enclosure 32. Accordingly, it is possible to further reliablyprevent condensation and/or frost on the surfaces of the dry evaporator22 and the large-sized printed circuit board 11 as well as the surfaceof the ductwork, defining the circulation channel 14 in the box-shapedenclosure 32.

[0191] In particular, if the dehydrator is made from zeolite, the dryatmosphere can be maintained in the box-shaped enclosure 32 for a longertime irrespective of the environment in which the large-sized computer10 is located. On the other hand, particles of nicotinic acid amid,often included in a smoke of cigarette, for example, tends todeteriorate silica gel. If silica gel is employed as the dehydrator, thelarge-sized computer 10 should be located in a clean environment.

[0192] As shown in FIG. 34, a heater 153 may be disposed in thebox-shaped enclosure 32 so as to heat the atmosphere in the box-shapedenclosure 32, for example. The heater 153 can be operated when thesemiconductor device module 12 is replaced or maintained. The heat fromthe heater 153 serves to heat the atmosphere within the box-shapedenclosure 32. When the atmosphere in the box-shaped enclosure 32 isheated, a rise in temperature can be established on the inner surface ofthe box-shaped enclosure 32 and the semiconductor device module 12. Ifthe semiconductor device enclosure unit 31, namely, the box-shapedenclosure 32 is opened after the atmosphere has been heated in theaforementioned manner, it is possible to prevent condensation on theinner surface of the box-shaped enclosure 32 and the semiconductordevice module 12. Since the rise in temperature can be accelerated ascompared with the natural radiation of heat, the working time ofreplacement or maintenance can remarkably be shortened.

[0193] In this case, heat exchangers 154, 155 may be disposed within thebox-shaped enclosure 43 of the semiconductor device enclosure unit 31,in addition to the aforementioned heater 153, as is apparent from FIG.34. The heat exchangers 154, 155 are coupled to the subsidiaryevaporator 23 and the circulation channel 14, respectively. The heater153 and the heat exchangers 154, 155 serve to control the temperature inthe box-shaped enclosure 32 during the operation of the refrigerationsystem 13. If the control in temperature by the heater 153 and the heatexchangers 154, 155 serves to prevent an excessive drop in temperature,the box-shaped enclosure 32 can be prevented from condensation and/orfrost on the outer surface. It is possible to reduce the thickness orvolume of a heat insulator, not shown, attached to the outer surface ofthe box-shaped enclosure 32, or completely omit such a heat insulator.If the aforementioned control in temperature serves to prevent anexcessive rise in temperature, the semiconductor device module 12 cancontinuously be cooled down in an efficient manner.

[0194]FIG. 35 illustrates the structure of the semiconductor deviceenclosure unit 31 according to another specific example. Thesemiconductor device enclosure unit 31 includes a first or innerbox-shaped enclosure 156 airtightly containing the large-sized printedcircuit board 11 and the dry evaporator 22 closely contacting thesemiconductor element on the large-sized printed circuit board 11, and asecond or outer box-shaped enclosure 157 airtightly containing the firstbox-shaped enclosure 156. A first dehumidifier 158 is attached to thefirst box-shaped enclosure 156 of the same structure as theaforementioned dehumidifier 33. Likewise, a second dehumidifier 159 isattached to the second box-shaped enclosure 157 of the same structure asthe aforementioned dehumidifier 33. The first dehumidifier 158 isdesigned to release moisture from the closed space within the firstbox-shaped enclosure 156 to the outside of the first box-shapedenclosure 156, namely, the closed space defined between the first andsecond box-shaped enclosures 156, 157 within the second box-shapedenclosure 157. The second dehumidifier 159 is designed to releasemoisture from the closed space within the second box-shaped enclosure157 to the open space outside the second box-shaped enclosure 157. Withthis arrangement, the moisture can reliably be released out of the firstbox-shaped enclosure 156 into the open space in an efficient manner.Even when the atmosphere in the first box-shaped enclosure 156 reaches acryogenic temperature, it is possible to reliably prevent condensationand/or frost within the first box-shaped enclosure 156.

[0195] As shown in FIG. 36, the aforementioned first dehumidifier 158may be attached to the second box-shaped enclosure 157 in theabove-described semiconductor device enclosure unit 31, for example. Anair duct 161 may be employed to connect the closed space within thefirst box-shaped enclosure 156 and the first dehumidifier 158 to eachother. The air duct 161 is designed to extend across the closed spacewithin the second box-shaped enclosure 157. Such location of the firstdehumidifier 158 contributes to reduction in the closed space within thesecond box-shaped enclosure 157, so that the second box-shaped enclosure157, namely, the entire semiconductor device enclosure unit 31 can bemade compact. It is preferable that the air duct 161 has an elasticityenough to deform to some extent.

[0196] In the case where the semiconductor device enclosure unit 31includes the first and second box-shaped enclosures 156, 157 asdescribed above, a common single door 165 is preferably attached to thefirst and second box-shaped enclosures 156, 157 so as to close togetheropenings 163, 164 defined in the first and second box-shaped enclosures156, 157, as shown in FIG. 37, for example. When the semiconductordevice module 12 is to be replaced or maintained, the closed spaceswithin the first and second box-shaped enclosure 156, 157 shouldsequentially be opened. The common single door 165 serves to allow theclosed spaces in the first and second box-shaped enclosures 156, 157 tobe opened with a single opening operation. Accordingly, the operabilitycan be improved at the time of replacement or maintenance for thesemiconductor device module 12. In place of the common single door 165,an interlocking mechanism 168 may be established between doors orflappers 166, 167 attached to the first and second box-shaped enclosures156, 157, respectively, as shown in FIG. 38, for example. Theinterlocking mechanism 168 is designed to cause the opening and closingmotion of the door 166 in response to the opening and closing motion ofthe door 167.

[0197]FIG. 39 schematically illustrates the structure of a refrigerationsystem of a closed cycle according to a second embodiment of the presentinvention. The refrigeration system 201 of this embodiment includes afirst circulation channel 205 extending from a first discharge port 203of a switching valve 202 to a first suction port 204 of the switchingvalve 202, and a second circulation channel 208 extending from a seconddischarge port 206 of the switching valve 202 to a second suction port207 of the switching valve 202. An accumulator 24, a compressor 15 andan oil separator 16 are sequentially connected in serial to the firstdischarge port 203 in the first circulation channel 105. The accumulator24, the compressor 15 and the oil separator 16 may have the samestructure as those included in the aforementioned refrigerant system 13of the first embodiment.

[0198] The second circulation channel 208 includes a first bidirectionalpassage 211 extending from the second discharge port 206 to a firstbifurcated point 210, first and second one-way passages 213, 214respectively extending from the first bifurcated point 210 to a secondbifurcated point 212, and a second bidirectional passage 215 extendingfrom the second bifurcated point 212 to the second suction port 207. Thefirst one-way passage 213 is designed to allow the refrigerant to flowfrom the first bifurcated point 210 to the second bifurcated point 212and restrain the flow of refrigerant from the second bifurcated point212 to the first bifurcated point 210. On the other hand, the secondone-way passage 214 is designed to restrain the flow of the refrigerantfrom the first bifurcated point 210 to the second bifurcated point 212and to allow the refrigerant to flow from the second bifurcated point212 to the second suction port 207. Check valves 216 may be incorporatedin the first and second one-way passages 213, 214, respectively, so asto achieve the aforementioned controlled flow of the refrigerant.

[0199] A condenser 17, a dry evaporator 22 and a subsidiary evaporator23 are incorporated in the first and second bidirectional passages 211,215 in the same manner as the aforementioned first embodiment. A firstexpansion valve 217 is likewise incorporated in the first one-waypassage 213 downstream of the receiver 18. Otherwise, a strainer 26 andan observation window 27 may likewise be incorporated in the firstone-way passage 213 in the aforementioned manner.

[0200] A receiver 218 is also incorporated in the second one-way passage214 downstream of the second bifurcated point 212. A second expansionvalve 219 is incorporated in the second one-way passage 214 downstreamof the receiver 218. The receiver 218 and the second expansion valve 219may have the same structure as the aforementioned receiver 18 and firstexpansion valve 217.

[0201] Assume that the switching valve 202 is operated to establishconnection between the first suction port 204 and the second dischargeport 206, as shown in FIG. 40, for example. In this case, the secondsuction port 207 is connected to the first discharge port 203 in theswitching valve 202. Accordingly, the refrigerant discharged from thesecond discharge port 206 is led to the second bidirectional passage 215through first bidirectional passage 211 and the first one-way passage213 during the operation of the compressor 15. The dry evaporator 22cools the semiconductor device module 12 in the aforementioned manner.The quality of the refrigerant in the dry evaporator 22 is maintained ata level below 1.0, for example, at a level below approximately 0.85. Ahigher performance of cooling can thus be established in the dryevaporator 22 in the aforementioned manner. The subsidiary evaporator 23serves to completely transform the refrigerant of gas-liquid mixturestate, discharged from the dry evaporator 22, into the refrigerant ofgas state, namely, the refrigerant gas.

[0202] Here, assume that the semiconductor device module 12 is to bereplaced or maintained. The semiconductor device enclosure unit 31should be opened prior to replacement or maintenance of thesemiconductor device module 12. As shown in FIG. 41, the switching valve202 is switched over, for example, before the semiconductor deviceenclosure unit 31 is opened. The changeover causes the first and secondsuction ports 204, 207 to be connected to each other in the switchingvalve 202. The refrigerant is allowed to flow out of the second suctionport 207 of the switching valve 202. The discharged refrigerant is ledto the first bidirectional passage 211 through the second bidirectionalpassage 215 and the second one-way passage 214.

[0203] When the refrigerant is allowed to circulate in the reversedirection in the second circulation channel 208 in this manner, the dryevaporator 22 and the subsidiary evaporator 23 are allowed to functionas a condenser, while the condenser 17 is forced to function as a dryevaporator. Accordingly, the dry evaporator 22 and the subsidiaryevaporator 23 heat the semiconductor device module 12, the large-sizedprinted circuit board 11 and the atmosphere within the semiconductordevice enclosure unit 31. If the semiconductor device enclosure unit 31,namely, the box-shaped enclosure 32 is opened to the open air afterheating has been effected by the evaporators 22, 23, condensation andthe like can reliably be prevented on the inner surface of thebox-shaped enclosure 32 and the semiconductor device module 12. Sincethe rise in temperature can be accelerated as compared with the naturalradiation of heat, the working time of replacement or maintenance canremarkably be shortened.

[0204] As is apparent from FIG. 39, a heater 221 is incorporated in therefrigeration system 201 in parallel with the dry evaporator 22 and thesubsidiary evaporator 23. The heater 221 is in general utilized onlywhen the refrigerant circulates along the second circulation channel 208in the reverse direction. The heater 221 serves to completely condensethe refrigerant directed to the receiver 218. A smaller heat transferarea can only be established in the dry evaporator 22 and the subsidiaryevaporator 23 as compared with the condenser 17 in the aforementionedrefrigeration system 201. Without the heater 221, an enough performanceof condensing cannot be achieved at the dry evaporator 22 and thesubsidiary evaporator 23 irrespective of a relatively higher performanceof cooling at the condenser 17.

[0205]FIG. 42 schematically illustrates a refrigeration system of aclosed cycle according to a third embodiment of the present invention.The refrigeration system 230 includes a circulation channel 14 in thesame manner as the aforementioned refrigeration system 13. A compressor15, a condenser 17, a receiver 18, an expansion valve 21, a dryevaporator 22, a subsidiary evaporator 23 and an accumulator 24, inaddition to the other components such as an oil separator 16 and astrainer 26, are incorporated in the circulation channel 14 in the samemanner as the refrigeration system 13.

[0206] The dry evaporator 22 includes a casing 232 contacting an targetheating object such as the semiconductor device module 12 at a verticalheat transfer plate 231, as shown in FIG. 42. A closed space orvaporization chamber 234 is defined between the heat transfer plate 231and a back plate 233 extending in parallel with the heat transfer plate231 in the casing 232. The vaporization chamber 234 is allowed to extendin a vertical direction along the heat transfer plate 231 from a bottomplate 235 upright to the heat transfer plate 231. The bottom plate 235is designed to extend in a horizontal direction from the heat transferplate 231 so as to reach the back plate 233 at the tip end. The casing232 may be made from a high heat conductive material such as a coppermaterial, for example.

[0207] A refrigerant inlet 236 is defined to open at the lowest positioninto the vaporization chamber 234 so as to introduce the refrigerantinto the vaporization chamber 234. A refrigerant outlet 237 is definedto open at the highest position into the vaporization chamber 234 so asto allow the refrigerant to flow out of the vaporization chamber 234. Afin aggregate 238 is integrally formed on the heat transfer plate 231 soas to define refrigerant passages extending in a vertical direction fromthe refrigerant inlet 236 to the refrigerant outlet 237, respectively.The structure of the fin aggregate 238 will be described later indetail.

[0208] The refrigeration system 230 is designed to allow a gas-liquidseparation at the vaporization chamber 234. The gas-liquid separationcan be achieved based on the flow or current of the refrigerant from aflow or current controller such as the expansion valve 21. A propermanagement on the operation of the compressor 15 and the expansion valve21 serves to control the flow or current of the refrigerant. Acontroller circuit or unit 239 can be employed to manage the operationof the compressor 15 and the expansion valve 21. The controller circuit239 is designed to calculate the compression ratio for the compressor 15based on the output received from pressure sensors 240, 241, forexample. The pressure sensors 240, 241 are incorporated in thecirculation channel 14 upstream and downstream of the compressor 15,respectively. The controller circuit 239 is also designed to utilize theoutput from a thermal sensor 242 and a pressure sensor 243 incorporatedin the circulation channel 14 downstream of the dry evaporator 22, forexample. If the gas-liquid separation can be achieved in this manner,the refrigerant liquid is allowed to stay on the bottom plate 235 withinthe vaporization chamber 234 under the influence of the gravity. Therefrigerant liquid is thus uniformly distributed into the respectiverefrigerant passages defined in the fin aggregate 238.

[0209] First and second jet nozzles 244, 245 are attached to the casing232 so as to insert the tip ends into the vaporization chamber 234,respectively. As is apparent from FIG. 42, the extension of the axialline of the first jet nozzle 244 is designed to interest the surface ofthe refrigerant liquid staying at the bottom of the vaporization chamber234 and is directed toward the fin aggregate 238. The second jet nozzle245 is designed to position its tip end or spout between the finaggregate 238 and the refrigerant inlet 236. A bypass duct defining abypass channel 247 is connected to the first and second jet nozzles 244,245. The bypass channel 247 is designed to diverge from the circulationchannel 14 downstream of the compressor 15 and the oil separator 16.

[0210] During the operation of the compressor 15, the refrigerant of gasstate, namely, the refrigerant gas, discharged from the compressor 15 ata high pressure, is supplied to the first and second jet nozzles 244,245 through the bypass channel 247. When the refrigerant gas is allowedto spout out of the first jet nozzle 244, the refrigerant liquidsplashes upward from the surface of the refrigerant liquid at the bottomof the vaporization chamber 234. The splashed refrigerant liquid isdirected to the fin aggregate 238. The splashed refrigerant liquid isallowed to stick to the fin aggregate 238 on the heat transfer plate231. In this manner, the refrigerant liquid is held on the heat transferplate 231 over a broader area. The vaporization of the refrigerant canbe promoted in the vaporization chamber 234.

[0211] When the refrigerant gas is supplied to the second jet nozzle 245through the bypass channel 237, the refrigerant gas is forced to spoutout of the second jet nozzle 245. The refrigerant gas serves to stir therefrigerant liquid at the bottom of the vaporization chamber 234. Suchstir of the refrigerant liquid in the vicinity of the refrigerant inlet236 contributes to a uniform influent of the refrigerant liquid into thevaporization chamber 234.

[0212] As is apparent from FIG. 42, an electronic controlled valve 248may be incorporated in the bypass channel 247 so as to control the flowor current of the refrigerant gas passing through the bypass channel247. The control of the flow or current in the bypass channel 247 isallowed to adjust the jet amount of the refrigerant gas introduced intothe vaporization chamber 234 at a high pressure. It is accordinglypossible to properly control the vapor pressure within the vaporizationchamber 234. If the vapor pressure can properly be controlled in thismanner, the boiling point of the refrigerant can properly be adjusted inthe vaporization chamber 234.

[0213] As shown in FIG. 43, the fin aggregate 238 includes a pluralityof fins 251 raised from the surface of the heat transfer plate 231 andextending in a vertical direction, for example. Micro channels 252 aredefined between the adjacent fins 251, respectively. The individualmicro channel 252 is designed to have a lateral width W1 enough torealize the capillary action of the refrigerant liquid. The finaggregate 238 serves to induce an ascent of the refrigerant liquid fromthe bottom of the vaporization chamber 234 along the micro channel 252.Accordingly, the fin aggregate 238, namely, the heat transfer plate 231is allowed to hold the refrigerant liquid over a broader areairrespective of the level L of the refrigerant liquid at the bottom ofthe vaporization chamber 234. The vaporization of the refrigerant liquidis thus be accelerated. It should be noted that the level Hr of theascent within the micro channel 252 can be controlled based on thesurface tension of the refrigerant liquid and the lateral width W1 ofthe micro channel 252.

[0214] Referring also to FIG. 44, the edges or ridgelines 253 of therespective fins 251 are designed to extend in parallel with each other.A datum line 254 is defined between the adjacent ridgelines 253 so as toextend in parallel with the adjacent ridgelines 253. A first wallsurface 255 extends from the ridgeline 253 of one of the adjacent fins251 to the common datum line 254, while a second wall surface 256extends from the ridgeline 253 of the other of the adjacent fins 251 tothe aforementioned common datum line 254. The first and second wallsurfaces 255, 256 are opposed to each other. The first and second wallsurfaces 255, 256 are connected to each other at the common datum line254. The first and second surface walls 255, 256 extend along the commondatum line 254.

[0215] The first and second wall surfaces 255, 256 comprises a curvedsurface extending from the ridgeline 253 to the datum line 254.Accordingly, the space between the first and second wall surfaces 255,256 gets larger as the first and second wall surfaces 255, 256 aredistanced apart from the common datum line 253, as is apparent from FIG.44. In this case, the refrigerant liquid exhibits a first surfacetension F1 at the surface opposed to the surface of the refrigerantliquid between the first and second wall surfaces 255, 256, based on theradius of curvature r of its surface and the relative angle a to thefirst and second wall surfaces 255, 256. On the other hand, therefrigerant liquid also exhibits a second surface tension F2 at thesurface opened to the ridgelines 253 based on the radius of curvature Rof its surface and the relative angle β to the first and second wallsurfaces 255, 256. As is extracted from the following equation, thefirst surface tension F1 is remarkably larger than the second surfacetension F2: $\begin{matrix}{{{F1} = \frac{2\sigma \quad \cos \quad \alpha}{r}}\operatorname{>>}{\frac{2{\sigma cos}\quad \beta}{R} = {F2}}} & \left\lbrack {{Equation}\quad 1} \right\rbrack\end{matrix}$

[0216] When the refrigerant liquid is squirted in the micro channel 252,a larger surface tension F1 can be generated at the surface of therefrigerant on the side of datum line 254, so that the refrigerantliquid is sucked toward the datum line 254, namely, into the bottom ofthe micro channel 252, based on the difference between the first andsecond surface tensions F1, F2. Consequently, a larger quantity of therefrigerant liquid can reliably be held between the first and secondwall surfaces 255, 256. The vaporization of the refrigerant liquid isthus promoted.

[0217] As shown in FIG. 45, the micro channel 252 may further include anexpanded groove 257 defined between the first and second wall surfaces255, 256, for example. The expanded groove 257 extends along the datumline 254. The expanded groove 257 serves to still reliably hold therefrigerant liquid introduced between the first and second wall surfaces255, 256. The vaporization of the refrigerant liquid can still furtherbe accelerated.

[0218] As shown in FIG. 46, the fin aggregate 238 may comprise aplurality of plate-shaped fins 258, in place of the aforementioned fins251, so as to hold the refrigerant liquid within the micro channels 252,for example. The plate-shaped fins 258 are designed to stand from thesurface of the heat transfer plate 231, respectively, so as to extend inparallel with each other at a pitch Pit smaller than 1.0 mm, forexample. A first wall surface 259 defined on one of the adjacentplate-shaped fins 258 serves to define the micro channel 252, incooperation with a second wall surface 260 defined on the other of theadjacent plate-shaped fins 258, between the adjacent plate-shaped fins258. The first and second wall surfaces 259, 260 are opposed to eachother. A thin rim saw, not shown, having a thickness equal to the groovewidth W of the micro channel 252, may be applied to the surface of theheat transfer plate 231 so as to form the micro channel 252, forexample. The thin rim saw serves to engrave the surface of the heattransfer plate 231 so as to shape the plate-shaped fins 258 on thesurface of the heat transfer plate 231. Alternatively, the plate-shapedfins 258 may be a thin plate of copper or aluminum, for example, fixedto the surface of the heat transfer plate 231.

[0219] First and second erosion surfaces may be provided on the firstand second wall surfaces 259, 260, respectively. A fine asperity can beestablished on the first and second erosion surfaces. Such a fineasperity serves to achieve an enlarged heat transfer area over theplate-shaped fins 258 and an improved wetness to the refrigerant liquid.The vaporization of the refrigerant liquid can still further beaccelerated. Erosive agent such as HF may be employed to form the firstand second erosion surfaces on the first and second wall surfaces 259,260, respectively.

[0220] Alternatively, heat conductive fine particles may be adhered tothe first and second wall surfaces 259, 260, respectively, so as toachieved an improved wetness. The size of the particles may be set atthe order of microns. The fine particles serve to achieve an enlargedheat transfer area over the plate-shaped fins 258 and an improvedwetness to the refrigerant liquid in the aforementioned manner. Thevaporization of the refrigerant liquid can thus be accelerated. The heatconductive fine particles may be made of any heat conductive materialsuch as diamond, gold, silver, carbon fibers, and the like.

[0221] The dry evaporator 22 employed in the aforementionedrefrigeration systems 13, 201, 230 according to the first, second andthird embodiments, may comprise a casing 302 attached to a small-sizedprinted circuit board 301 extending in the horizontal direction, and acooling element or elements, namely, pistons 303 incorporated in thecasing 302, as shown in FIG. 47, for example. The casing 302 is designedto receive the connection of a inlet duct 304 and an outlet duct 305extending in a vertical direction, respectively. The inlet and outletducts 304, 305 are coupled to the casing 302 through couplers 306.

[0222] As is apparent from FIG. 48, a refrigerant passage 309 is definedbetween a top plate 307 and a bottom plate 308 extending in parallel inthe horizontal direction in the casing 302. A refrigerant is introducedinto the refrigerant passage 309 through a refrigerant introductionpassage defined in the inlet duct 304. After passing through therefrigerant passage 309, the refrigerant is allowed to flow out througha refrigerant discharge passage defined in the outlet duct 305. Thepistons 303 are designed to extend across the refrigerant passage 309 bypenetrating through the top and bottom plates 307, 308 of the casing302, respectively. The piston 303 is allowed to protrude its tip end outof the casing 302 so as to contact a semiconductor element 310 at thetip end. The piston 303 may be made from a high heat conductive materialsuch as a copper material.

[0223] Sealing members 311 are attached around the piston 303. Thesealing members 311 are interposed between the top plate 307 and thepiston 303 as well as between the bottom plate 308 and the piston 303.The sealing members 311 serve to prevent any leakage of the refrigerantthrough connections between the top plate 307 and the piston 303 as wellas between the bottom plate 308 and the piston 303. A spring 312 may beadded to the casing 302 so as to bias the piston 303 against the surfaceof the semiconductor element 310.

[0224] Heat generated at the semiconductor element 310 is efficientlytransferred to the refrigerant through the pistons 303 in the dryevaporator 22. The semiconductor element 310 can efficiently be cooleddown. If the casing 302 is made from a heat insulating material such asa synthetic resin, heat is solely transferred to the refrigerant throughthe pistons 303. A performance of cooling can further be improved in thedry evaporator 22.

[0225] As shown in FIG. 49, the refrigerant passage 309 may be defined,common to all of the pistons 303, in the casing 302, for example.Alternatively, the refrigerant passage 309 may be divided into rowscorresponding to the respective rows of the pistons 303, as shown inFIG. 50.

[0226] As shown in FIG. 51, a single or plurality of fins 313 may beattached to the piston 303 so as to encircle the piston 303, forexample. The fins 313 are designed to extend in the horizontal directionfrom the cylindrical periphery of the piston 303 within the refrigerantpassage 309. The fins 313 serve to increase the heat transfer areabetween the refrigerant and the piston 303, so that heat of thesemiconductor element 310 can still efficiently be transferred to therefrigerant through the piston 303 and the fins 313. The fins 313 may beintegral to the piston 303.

[0227] Furthermore, the size or extension of the individual fin 313 canbe adjusted in the dry evaporator 22 based on the quantity of heatgenerated at the corresponding semiconductor element 310, as shown inFIG. 52, for example. As conventionally known, enlargement of the fin313 realizes an increase in the heat transfer area between the piston303 and the refrigerant, so that a larger quantity of heat can betransferred from the piston 303 to the refrigerant. The fin 313 of thesize following variation in the quantity of heat contributes touniformity in temperature of the semiconductor elements 310. In otherwords, even if variation is found in the quantity of heat generated atthe respective semiconductor elements 310, all of the semiconductorelements 310 can efficiently be cooled down over the entire area of thesingle small-sized printed circuit board 301. It should be noted thatthe heat transfer area or surface area of the fin 313 for a singlepiston 303 can be controlled not only by the size of the fin 313 in thismanner but also by the number of the fins 313 attached to the piston303.

[0228] Furthermore, the dry evaporator 22 may comprise a block member315 attached to the small-sized printed circuit board 301 extending inthe horizontal direction, as shown in FIG. 53, for example. The blockmember 315 is provided with columnar through bores 316 extending in avertical direction, and through hole path 317 extending in thehorizontal direction so as to cross the columnar through bores 316. Thecolumnar through bores 316 are formed to correspond to the respectivesemiconductor elements 310 on the small-sized printed circuit board 301.The columnar through bores 316 and the through hole path 317 may bemachined with a drill in a facilitated manner. The block member 315functions as a casing defining a refrigerant passage inside.

[0229] A cooling element or piston 318 is inserted into the individualcolumnar through bore 316. The piston 318 is designed to protrude itstip end out of the block member 315. The tip end of the piston 318 isallowed to contact the surface of the semiconductor element 310. Thepiston 318 may be made from a high heat conductive material such as acopper material.

[0230] A refrigerant passage 319 is defined between the outercylindrical periphery of the piston 318 and the inner surface of thecolumnar through bore 316 so as to lead the refrigerant along the outerperiphery of the piston 318. The refrigerant passage 319 is designed toconnect a pair of the through hole paths 317, opened at opposite innersurfaces of the columnar through bore 316, to each other.

[0231] Upper and lower sealing members or O-rings 321 is fitted on theouter cylindrical periphery of the piston 318. The upper and lowerO-rings 321 are designed to define boundaries of the refrigerant passage319. The refrigerant flowing along the outer periphery of the piston 318can be prevented from leaking out of the refrigerant passage 319.

[0232] As is apparent from FIG. 54, a pair of guide grooves 322 aredefined on the outer periphery of the piston 318 so as to extend in avertical direction along the meridian of the piston 318. Connectinggrooves 323 are also defined on the outer periphery of the piston 318 soas to connect the lower ends of the guide grooves 322 to each other.When the piston 318 is received in the columnar through bore 316, theguide grooves 322 and the connecting grooves 323 serve to define theaforementioned refrigerant passage 319 in cooperation with the innersurface of the columnar through bore 316.

[0233] Referring again to FIG. 53, when the refrigerant is introducedinto the through hole path 317, the refrigerant is allowed to flow intothe upstream guide groove 322 and to fall along the outer periphery ofthe piston 318. The refrigerant then flows through the connecting groove323 into the downstream guide groove 322. This time, the refrigerant isallowed to ascend along the outer periphery of the piston 318 in thedownstream guide groove 322. Thereafter, the refrigerant is introducedinto the next through hole path 317. The flow of the refrigerant alongthe outer periphery of the piston 318 serves to realize a higherperformance of cooling the piston 318. In addition, a plurality of fins324 may be formed within the guide groove 322 so as to extend inparallel with each other in a vertical direction along the meridian,respectively, as shown in FIG. 55, for example. The fins 324 contributesto a further enlargement of the heat transfer area between the piston318 and the refrigerant, so that a still higher performance of coolingcan be established for the piston 318.

[0234] As shown in FIG. 56, a connecting hole 326 may be formed in thepiston 318 so as to connect a pair of guide grooves 322 to each other,in place of the connecting groove 323, for example. The connecting hole326 may include a central bore 327 extending in the axial direction ofthe piston 318 along the central axis of the piston 318, and a pair ofradial bores 328 extending in a radial direction from the central bore327 so as to open at the corresponding guide grooves 322, respectively,as is apparent from FIG. 57.

[0235] It is preferable that the radial bores 328 are located at adistance as much as possible on the piston 318. A larger distancebetween the radial bores 328 contributes to an increase in the heattransfer area between the inner surface of the central bore 327 and therefrigerant. Accordingly, a still higher performance of cooling can beachieved at the piston 318. In this case, the upper and lower throughhole paths 317 a, 317 b may be defined in the block member 315 so as tocross the columnar through bore 316, as is apparent from FIG. 56. Therefrigerant is allowed to alternately flow through the upper and lowerthrough hole paths 317 a, 317 b between the adjacent pistons 318 in theentire block member 315.

[0236] The connecting bore 326 may be formed with a simple machiningutilizing a drill, for example. First of all, a first raw bore 332 isdrilled in a piston material 331 from its end surface along the centralaxis of the piston material 331, as shown in FIG. 58A. Second raw bores333 are then drilled in the piston material 331 from the outercylindrical surface along the radial direction, as shown in FIG. 58B.Finally, a plug 334 is inserted into the first raw bore 332 at the endsurface of the piston material 331, as shown in FIG. 58C. The centralbore 327 is thus defined in the first raw bore 332.

[0237] As shown in FIG. 59, a helical guide groove 335 may be defined onthe outer cylindrical surface of the piston 318, in place of theaforementioned guide groove 322, for example. When the piston 318 ofthis type is received in the columnar through bore 316, as shown in FIG.60, the refrigerant passage 319 can be defined between the guide groove335 and the inner surface of the columnar through bore 316. Therefrigerant introduced into the through hole path 317 a is allowed toflow downward along the guide groove 335 tracing the helical path. It isthus possible to increase the heat transfer area between the piston 318and the refrigerant. A higher performance of cooling can be accomplishedfor the piston 318. The refrigerant is allowed to flow out into thethrough hole path 317 b. The next piston 318 allows the refrigerant toflow upward along the guide groove 335 tracing the helical path.Likewise, a higher performance of cooling can also be accomplished forthe next piston 318. The refrigerant is allowed to reach the throughhole path 317 a.

[0238] Furthermore, a connecting hole 336 may also be formed in thepiston 318, in addition to the aforementioned guide groove 335, as shownin FIG. 61. The connecting hole 336 is designed to include, as shown inFIG. 62, a central bore 337 extending in the axial direction of thepiston 318 along the central axis of the piston 318, and a first radialbore 338 extending in a radial direction from the central bore 337 so asto open at the end of the guide groove 335, as well as a second radialbore 339 likewise extending in a radial direction from the central bore337 so as to open at the outer cylindrical surface of the piston 318.The central bore 337 and the first and second radial bores 338, 339 maybe formed in the same manner as the aforementioned central bore 327 andradial bores 328.

[0239] As is apparent from FIG. 62, the connecting hole 336 allows therefrigerant to flow downward along the guide groove 335 tracing thehelical path so as to finally reach the through hole path 317.Accordingly, even when the guide groove 335 of the helical path isemployed in the aforementioned manner, it is not necessary to form apair of the upper and lower through hole paths 317 a, 317 b in the blockmember 315 between the adjacent pistons 318.

[0240] Furthermore, a plurality of through hole paths 341 may be formedin the piston 318 so as to accept the flow of the refrigerant, as shownin FIG. 63. The through hole paths 341 serves to increase the heattransfer area between the piston 318 and the refrigerant. Heat of thepiston 318 can be transferred to the refrigerant in an efficient manner.

[0241] Moreover, the opposite ends of the individual through hole path341 is designed to open at first and second flat surfaces 342, 343formed within a plane including a pair of meridians on the outercylindrical surface of the piston 318. When the piston 318 is receivedin the columnar through bore 316, a refrigerant introduction chamber 345can be defined between the first flat surface 342 and the inner surfaceof the columnar through bore 316, as shown in FIG. 64. Likewise, arefrigerant discharge chamber 346 can be defined between the second flatsurface 343 and the inner surface of the columnar through bore 316. Therefrigerant introduction and discharge chambers 345, 346 serve touniformly distribute the refrigerant into the respective through holepaths 341.

[0242] When the circulation channel 14 can be divided into sections withthe assistance of the couplers 34 in the aforementioned manner, anair-purge mechanism 351 is preferably incorporated in the circulationchannel 14, as shown in FIG. 65, for example. The air-purge mechanism351 may include first and second shut-off valves 352, 353 incorporatedin the circulation channel 14 upstream and downstream of the coupler 34,respectively, and a bidirectional switching valve 354 incorporated inthe circulation channel 14 between the coupler 34 and the secondshut-off valve 353. The bidirectional switching valve 354 is providedwith a straight path 355 connecting the upstream circulation channel 14a and the downstream circulation channel 14 b to each other, and an openpath 356 bifurcated from the straight path 355. The open path 356 isdesigned to connect the straight path 355 to the open air. When thebidirectional switching valve 354 is set in a normal mode, the open path356 is shut off from the straight path 355, as shown in FIG. 65. Thestraight path 355 connects the upstream and downstream circulationchannels 14 a, 14 b to each other. On the other hand, when thebidirectional switching valve 354 is changed over to an activation mode,the upstream and downstream circulation channels 14 a, 14 b are shut offfrom each other, as shown in FIG. 66. The upstream circulation channel14 a is connected to the open path 356.

[0243] During the operation of the refrigeration system 13, thebidirectional switching valve 354 is set in the normal mode.Simultaneously, the first and second shut-off valves 352, 353 are keptopen. The refrigerant is allowed to circulate in the overall circulationchannel 14 in response to the action of the compressor 14.

[0244] When the connection of the couplers 34 are to be released, thebidirectional switching valve 354 is still kept in the normal mode. Noair can be introduced into the circulation channel 14 through the openpath 356. As long as the self-sealing mechanism is active for thecouplers 34, no air can be introduced into the circulation channel 14.The first and second shut-off valves 352, 353 may be kept open orclosed.

[0245] When the couplers 34 are to be connected, the first and secondshut-off valves 352, 353 must be closed. After the couplers 34 have beenconnected to each other, the bidirectional switching valve 354 ischanged over to the activation mode. The upstream circulation channel 14a is opened to the open air. Simultaneously, the first shut-off valve352 is opened. In this situation, when the compressor 15 operates, airremaining in the upstream circulation channel 14 a can be purged out ofthe open path 356 into the open air in response to the pressure appliedto the refrigerant. After the air has completely been purged out, thebidirectional switching valve 354 is changed over to the normal mode.Consequently, the circulation channel 14 is shut out from the open air.

[0246] Thereafter, the second shut-off valve 353 is opened. The overallclosed circulation channel 14 can thus be established. The purge of theair out of the circulation channel 14 in this manner reliably preventsintroduction of air even when the connection and disconnection of thecouplers 34 are repeated. No deficiency due to introduction of air isinduced in the refrigeration system 13. As conventionally known,introduction of air into the circulation channel 14 causes trouble orfailure in the refrigeration system 13.

[0247] It is preferable that the bidirectional switching valve 354 andthe second shut-off valve 353 are combined or unified in theaforementioned air-purge mechanism 351. If a single mechanism can beestablished to achieve the functions of the bidirectional switchingvalve 354 and the second shut-off valve 353, a section of thecirculation channel 14 can be omitted between the bidirectionalswitching valve 354 and the second shut-off valve 353, so thatintroduction of air into the circulation channel 14 can still reliablybe prevented.

[0248]FIG. 67 schematically illustrates the structure of a refrigerationsystem of a closed cycle according to a fourth embodiment of the presentinvention. The refrigeration system 361 further includes a gas-liquidseparation filter 363 incorporated in a refrigerant outlet 362 of thedry evaporator 22 so as to maintain the quality of the refrigerant atlevel smaller than 1.0, specifically, approximately 0.85 within the dryevaporator 22. The gas-liquid separation filter 363 is designed to allowonly the refrigerant of gas state, namely, the refrigerant gas to flowdownstream. Accordingly, even when the refrigerant liquid is notcompletely evaporated in the dry evaporator 22, the compressor 15 canreliably be prevented from a compression of a liquid without increasinga load to a gas-liquid separator such as the accumulator 24. Moreover,the gas-liquid separation filter 363 enables omission of theaforementioned subsidiary evaporator 23. However, the gas-liquidseparation filter 363 may be employed in combination with theaforementioned subsidiary evaporator 23 in the refrigeration systems. Inthis description of the fourth embodiment, the like reference numeralsare attached to structures achieving function or effect identical tothose of the aforementioned first embodiments. Duplicate description maybe omitted.

What is claimed is:
 1. A refrigeration system comprising: a circulationchannel through which a refrigerant circulates; and a dry evaporatorincorporated in the circulation channel and designed to keep a qualitysmaller than 1.0 in evaporating the refrigerant.
 2. The refrigerationsystem according to claim 1 , further comprising a subsidiary evaporatorincorporated in the circulation channel downstream of the dryevaporator.
 3. The refrigeration system according to claim 1 , furthercomprising: a refrigerant outlet defined in the dry evaporator fordischarging the refrigerant of gas-liquid mixture state; and agas-liquid separation filter incorporated in the refrigerant outlet. 4.A refrigeration system comprising: a circulation channel through which arefrigerant circulates; a dry evaporator incorporated in the circulationchannel and contacting a target heating object; and a subsidiaryevaporator incorporated in the circulation channel downstream of the dryevaporator.
 5. A method of refrigeration comprising: vaporizing arefrigerant within a dry evaporator incorporated in a circulationchannel, through which the refrigerant circulates, so as to allow therefrigerant of gas-liquid mixture state to flow out of the dryevaporator.
 6. The method of refrigeration according to claim 5 ,further comprising heating the refrigerant flowing out of the dryevaporator so as to completely evaporate the refrigerant of liquidstate.
 7. A dry evaporator for a refrigeration system, comprising: acasing defining a closed space; a refrigerant inlet defined in thecasing so as to open at a wall surface; a refrigerant outlet defined inthe casing so as to open at a wall surface; and a group of fins inwardlyprotruding from an inner surface of the casing so as to define aplurality of refrigerant passages extending in parallel from therefrigerant inlet toward the refrigerant outlet, respectively, whereinthe refrigerant passage gets shorter at a position remoter from astraight line extending from the refrigerant inlet to the refrigerantoutlet.
 8. A dry evaporator for a refrigeration system, comprising: acasing defining a closed space; a refrigerant inlet defined in thecasing so as to open at a wall surface; a refrigerant outlet defined inthe casing so as to open at a wall surface; and a group of fins inwardlyprotruding from an inner surface of the casing so as to define aplurality of refrigerant passages extending in parallel from therefrigerant inlet toward the refrigerant outlet, respectively, whereinthe refrigerant passage gets wider at a position remoter from a straightline extending from the refrigerant inlet to the refrigerant outlet. 9.A dry evaporator for a refrigeration system, comprising: a casingdefining a closed space between a top plate and a bottom plate andcontacting a target heating object at the bottom plate; an intermediateplate disposed between the top and bottom plates within the closedspace; a vaporization chamber defined between the intermediate andbottom plates; a refrigerant inlet defined in the top plate; anintroduction chamber defined between the top and intermediate plates andextending from the refrigerant inlet toward the vaporization chamber;and a discharge chamber defined between the top and intermediate platesand extending from the vaporization chamber toward the refrigerantoutlet.
 10. The dry evaporator for a refrigeration system according toclaim 9 , wherein a space between the top and intermediate plates is setsmaller than a space between the bottom and intermediate plates.
 11. Thedry evaporator for a refrigeration system according to claim 10 ,further comprising: an introduction opening defined by an edge of theintermediate plate and designed to connect the introduction andvaporization chambers to each other; and a dike extending along the edgeof the intermediate plate so as to swell from the intermediate plate atits surface receiving a refrigerant within the introduction chamber. 12.The dry evaporator for a refrigeration system according to claim 9 or 10, wherein the introduction chamber is designed to by degree expand as itgets closer to the vaporization chamber.
 13. The dry evaporator for arefrigeration system according to claim 12 , wherein the dischargechamber is designed to by degree narrow as it gets closer to therefrigerant outlet.
 14. The dry evaporator for a refrigeration systemaccording to claim 9 or 10 , wherein a plurality of refrigerant passagesare defined within the introduction chamber so as to respectively extendfrom the refrigerant inlet toward the vaporization chamber.
 15. The dryevaporator for a refrigeration system according to claim 14 , anexpanded passage is connected to a downstream end of the refrigerantpassage.
 16. A dry evaporator for a refrigeration system, comprising: acasing defining a closed space between a top plate and a bottom plateand contacting a target heating object at the bottom plate; anintermediate plate disposed between the top and bottom plates within theclosed space and connected to an inner surface of the casing; avaporization chamber defined between the intermediate and bottom plates;a discharge chamber defined between the top and intermediate plates; aninlet duct defining a refrigerant introduction passage penetratingthrough the discharge chamber so as to reach the vaporization chamber;and an outlet duct surrounding the inlet duct so as to define arefrigerant discharge passage extending from the discharge chamber. 17.A refrigeration system comprising: a circulation channel through which arefrigerant circulates; a dry evaporator incorporated in the circulationchannel and contacting a target heating object at its bottom plate; avaporization chamber defined within the dry evaporator for inducing aflow of the refrigerant along the bottom plate in a horizontaldirection; and a flow controller incorporated in the circulation channelfor discharging the refrigerant at a flow enough to establish agas-liquid separation within the vaporization chamber.
 18. A dryevaporator for a refrigeration system, comprising: a casing contacting atarget heating object at a vertical heat transfer plate; a vaporizationchamber defined adjacent the heat transfer plate within the casing; arefrigerant inlet opened at an inner surface of the vaporizationchamber; a refrigerant outlet opened at the inner surface of thevaporization chamber at a location above the refrigerant inlet; and aplurality of fins integrally formed on the heat transfer plate withinthe vaporization chamber so as to define a plurality of refrigerantpassages respectively extending in a vertical direction from therefrigerant inlet toward the refrigerant outlet.
 19. The dry evaporatorfor a refrigeration system according to claim 18 , further comprising: abypass opening formed in the casing so as to open at a lowest positionin the vaporization chamber; a duct connected to the casing so as todefine a discharge channel extending from the refrigerant outlet; and abypass channel connecting the bypass opening and the discharge channelto each other.
 20. A refrigeration system comprising: a circulationchannel through which a refrigerant circulates; a dry evaporatorincorporated in the circulation channel and contacting a target heatingobject at its vertical heat transfer plate; a vaporization chamberdefined adjacent the heat transfer plate within the dry evaporator; arefrigerant inlet opened at an inner surface of the vaporizationchamber; a refrigerant outlet opened at the inner surface of thevaporization chamber at a location above the refrigerant inlet; aplurality of fins integrally formed on the heat transfer plate withinthe vaporization chamber so as to define a plurality of refrigerantpassages respectively extending in a vertical direction from therefrigerant inlet toward the refrigerant outlet; and a flow controllerincorporated in the circulation channel for discharging the refrigerantat a flow enough to establish a gas-liquid separation within thevaporization chamber.
 21. The refrigeration system according to claim 20, further comprising: a bypass opening formed in the dry evaporator soas to open at a lowest position in the vaporization chamber; a ductconnected to the dry evaporator so as to define a discharge channelextending from the refrigerant outlet; and a bypass channel connectingthe bypass opening and the discharge channel to each other.
 22. A dryevaporator for a refrigeration system, comprising: a casing defining avaporization chamber between a vertical heat transfer plate and avertical back plate and contacting a target heating object at the heattransfer plate; a partition plate disposed between the heat transferplate and the back plate so as to divide an upper portion of thevaporization chamber into an introduction space adjacent the heattransfer plate and a discharge space adjacent the back plate; arefrigerant inlet opened at an inner surface of the introduction space;and a refrigerant outlet opened at an inner surface of the dischargespace; wherein a depth of a lower portion of the vaporization chamber isset larger than a space measured between the heat transfer plate and thepartition plate, said depth measured from a lower edge of the partitionplate in a vertical direction.
 23. A refrigeration system comprising: acirculation channel through which a refrigerant circulates; a dryevaporator incorporated in the circulation channel and defining avaporization chamber between a vertical heat transfer plate and avertical back plate; a partition plate disposed between the heattransfer plate and the back plate so as to divide an upper portion ofthe vaporization chamber into an introduction space adjacent the heattransfer plate and a discharge space adjacent the back plate; arefrigerant inlet opened at an inner surface of the introduction space;a refrigerant outlet opened at an inner surface of the discharge space;and a flow controller incorporated in the circulation channel fordischarging the refrigerant at a flow enough to establish a gas-liquidseparation within the vaporization chamber, wherein a depth of a lowerportion of the vaporization chamber is set larger than a space measuredbetween the heat transfer plate and the partition plate, said depthmeasured from a lower edge of the partition plate in a verticaldirection.
 24. A dry evaporator for a refrigeration system, comprising:a casing contacting a target heating object at a vertical heat transferplate; and a micro channel formed on the heat transfer plate within thecasing so as to extend in a vertical direction, said micro channelhaving a width enough to realize a capillary action of a refrigerant.25. A refrigeration system comprising: a circulation channel throughwhich a refrigerant circulates; a dry evaporator incorporated in thecirculation channel and contacting a target heating object at a verticalheat transfer plate; a micro channel formed on the heat transfer platewithin the dry evaporator so as to extend in a vertical direction, saidmicro channel having a width enough to realize a capillary action of arefrigerant; and a flow controller incorporated in the circulationchannel for discharging the refrigerant at a flow enough to establish agas-liquid separation within the dry evaporator.
 26. A dry evaporatorfor a refrigeration system, comprising: a casing contacting a targetheating object at a heat transfer plate; a first wall surface defined onthe heat transfer plate within the casing so as to extend from a datumline; a second wall surface connected to the first wall surface at thedatum line and opposed to the first wall surface, a space between thefirst and second wall surfaces getting larger as said second wallsurface is distanced apart from the datum line; and a micro channeldefined between the first and second wall surfaces so as to establish acapillary action of a refrigerant.
 27. The dry evaporator for arefrigeration system according to claim 26 , wherein an expanded grooveis defined at least on any of the first and second wall surfaces so asto extend along the datum line.
 28. A dry evaporator for a refrigerationsystem, comprising: a casing contacting a target heating object at aheat transfer plate; a first erosion surface defined on the heattransfer plate within the casing; and a second erosion surface opposedto the first erosion surface so as to define a micro channel between thefirst and second erosion surfaces.
 29. A dry evaporator for arefrigeration system, comprising: a casing contacting a target heatingobject at a heat transfer plate; a first wall surface defined on theheat transfer plate within the casing; a second wall surface opposed tothe first wall surface so as to define a micro channel between the firstand second wall surfaces; and heat conductive fine particles adhered tothe first and second wall surfaces, respectively.
 30. A refrigerationsystem comprising: a circulation channel through which a refrigerantcirculates; a compressor incorporated in the circulation channel anddesigned to discharge the refrigerant of gas state at a high pressure; adry evaporator incorporated in the circulation channel so as to contacta target heating object at a heat transfer plate; a jet nozzle insertinga tip end into an interior of the dry evaporator; and a bypass channeldiverging from the circulation channel downstream of the compressor soas to supply the refrigerant of gas state toward the jet nozzle.
 31. Therefrigeration system according to claim 30 , wherein a flow controlleris incorporated in the bypass channel.
 32. A semiconductor device modulecomprising: a printed circuit board; a semiconductor element mounted onthe printed circuit board; a dry evaporator contacting the semiconductorelement and applicable to a refrigeration system of a closed cycle; anda heat insulator member containing the dry evaporator so as to fix thedry evaporator to the printed circuit board.
 33. The semiconductordevice module according to claim 32 , wherein said heat insulator membercomprises a first half piece containing the printed circuit board, and asecond half piece containing the dry evaporator and detachably coupledto the first half piece.
 34. The semiconductor device module accordingto claim 32 or 33 , wherein a heater is incorporated in the heatinsulator member.
 35. The semiconductor device module according to claim34 , wherein a heat conductive member is interposed between the heaterand the dry evaporator, said heat conductive member having a propertyallowing heat to conduct at a first specific thermal conductivity in avertical direction oriented from the heater to the dry evaporator and toconduct at a second specific thermal conductivity larger than the firstspecific thermal conductivity in a plane perpendicular to the verticaldirection.
 36. A semiconductor device module comprising: a printedcircuit board; a semiconductor element mounted on an upper side of theprinted circuit board; a dry evaporator contacting the semiconductorelement and applicable to a refrigeration system of a closed cycle; aninput/output pin standing on a lower side of the printed circuit board;and a heater attached to the lower side of the printed circuit board.37. A semiconductor device module comprising: a printed circuit board; asemiconductor element mounted on an upper side of the printed circuitboard; a dry evaporator contacting the semiconductor element andapplicable to a refrigeration system of a closed cycle; an input/outputpin standing on a lower side of the printed circuit board; and a heatinsulator member containing the input/output pin.
 38. A semiconductordevice module comprising: a printed circuit board; a semiconductorelement mounted on the printed circuit board; a heat transfer platecontacting the semiconductor element; a dry evaporator contacting theheat transfer plate and applicable to a refrigeration system of a closedcycle; a bolt for fixation received in a through bore defined in theheat transfer plate; and a low heat conductive member interposed betweenthe heat transfer plate and the bolt.
 39. A semiconductor device modulecomprising: a printed circuit board; a semiconductor element mounted onthe printed circuit board; a dry evaporator contacting the semiconductorelement and applicable to a refrigeration system of a closed cycle; anda heater contacting the dry evaporator.
 40. A semiconductor devicemodule comprising: a printed circuit board; a semiconductor elementmounted on the printed circuit board; a heat transfer plate contactingthe semiconductor element; a dry evaporator contacting the heat transferplate and applicable to a refrigeration system of a closed cycle; and aheater contacting the heat transfer plate.
 41. The semiconductor devicemodule according to claim 39 or 40 , wherein a thermal sensor is mountedon the printed circuit board.
 42. A connector for a semiconductor devicemodule, comprising: an electric conductive member receiving aninput/output pin protruding from the semiconductor device module; and aheater disposed to surround the electric conductive member.
 43. Asemiconductor device enclosure unit comprising: a box-shaped enclosuredesigned to contain a dry evaporator contacting a semiconductor elementon a printed circuit board; and a dehumidifier designed to releasemoisture from a closed space defined in the box-shaped enclosure to anopen space outside the box-shaped enclosure.
 44. The semiconductordevice enclosure unit according to claim 43 , wherein a heater isattached to an inner surface of the box-shaped enclosure.
 45. Asemiconductor device enclosure unit comprising: a first box-shapedenclosure designed to contain a dry evaporator contacting asemiconductor element on a printed circuit board; a second box-shapedenclosure designed to contain the first box-shaped enclosure; a firstdehumidifier designed to release moisture from a closed space defined inthe first box-shaped enclosure to an outside; and a second dehumidifierdesigned to release moisture from a closed space within the secondbox-shaped enclosure to an open space outside the second box-shapedenclosure.
 46. The semiconductor device enclosure unit according toclaim 45 , wherein a heater is attached to at least an inner surface ofthe first box-shaped enclosure.
 47. A semiconductor device modulecomprising: a printed circuit board; a semiconductor element mounted onthe printed circuit board; a casing attached to the printed circuitboard and designed to define a refrigerant passage; and a coolingelement extending across the refrigerant passage and designed toprotrude its tip end out of the casing, said tip end contacting thesemiconductor element.